you're about to learn how to program in

Java from Farhan hassin children Farhan

is an experience­d software developer

here at free code camp and he is great

at breaking down concepts for beginners

this is a great course if you want to

learn Java and you can follow along with

the whole course from within your web

browser Farhan will teach you the basics

of java using replit replit is an online

IDE that allows people to write all

sorts of programmin­g languages right

within their web browser and repl

provided a grant that made this course

possible so it's time to learn Java

hello everyone welcome to the Java for

beginners course I am Farhan Hassan

chodri and in this course I will teach

you all the fundamenta­l concepts around

Java now ideally a programmin­g course

usually starts by downloadin­g and

installing a lot of sdks or Ides or

whatnot but since we will be using

rapidly throughout the entire course we

don't need to do any of those replete is

an online collaborat­ive IDE that you can

use right from your browser to start go

www.reply.­com and you should land on the

page you can create an account on

replete or if you already have an

account just go ahead and log into that

I will just use my Google account to log

in once you have logged in you will land

on your home page from here you can

create a new Ripple by using this create

now from the list of language we will

pick Java but just so that you know

refleet supports a long list of

languages make sure you are giving your

new Rebels some descriptiv­e names such

finally hit the create triple button and

wait until the process finishes

now if you have worked with some other

code editors such as Visual Studio code

the look of replete should not be very

different to you you can change its

default layout by going to settings

and default layout by default it should

but you can also pick stacked if you

like that layout Now the default Java

Ripple usually comes with a bunch of

code and you may have already guessed

that this is the famous hello world

program written in Jaffa to run this

code click on this run button here

and you will see the code's output on

there you go congratula­tions on creating

and running your first Rebel on the next

lesson I will explain what's going on

remember you can always run replay dark

by clicking on this Moon icon and if you

prefer dark themes over the lighter ones

the hello world program is probably the

simplest executable Java program that

you can write yet it's very important

that you understand each part of this

as you may have already guessed source

files in Java end with the dot Java

extension and compiled byte codes

usually end with the dot class extension

to see the compiled byte codes on replay

click on these three dots on the files

menu and click on show hidden files

the program starts with a class

declaratio­n a class is a collection of

related code in Java in every Java

source file that is the file with the

dot Java extension you can have one top

level public class and that class has to

match the name of the source file this

is because if you have multiple classes

you will see that the Java compiler

produces individual byte cores for each

to avoid any confusion about which of

these classes is the entry point to the

program the jvm is designed to treat the

bytecode that matches the name of the

source file as the entry point

inside the class there is a main method

those of you familiar with C C plus plus

or go may already know that the main

method or function serves as the NG

the jvm is programmed in a way that it

will specifical­ly look for a static

method that is named main has Public

Access takes an array of string as a

parameter and doesn't return any value

so you will have to write your main

method as public static void main string

one thing that you can change however is

the array holds the command line

arguments passed to the program upon

system.out­.print element method prints

out whatever string you pass to it as an

argument unlike python or JavaScript

semicolons are mandatory in Java so if

you leave it out the program will fail

that's pretty much it about the hello

world program don't worry if you didn't

understand all the terms used in this

lesson you will have a much better idea

about topics like public and private

access modifiers Statics classes methods

now if you try to run the program using

everything works out just as expected

another thing that you can change is the

this will make sure that replit opens

the correct Java source file whenever

you decide to return to this project

now there are a lot of other options in

this dot replete file but those are not

the hello world program you have been

seeing so far is pretty simple if you

want to write more complex programs you

will at least need some understand­ing of

variables variable is any entity that

can take on different values for example

if you want to store your age inside a

variable you can do so like this

first you will have to write the type of

the variable age is an integer or int

then you will have to write the name of

the variable which is age in this case

then you can finish off by putting a

you just declared a variable declaring

means the compiler will know that this

variable exists however you will also

need to Define it you can do so by

assigning a value to this variable like

write the name of the variable then an

equal sign followed by your desired

in this case the equal sign is known as

an assignment operator we'll learn about

operator in lot more detail in lateral

lessons now you can print out the

variable to the console like this

and just in case you are wondering using

a plus sign is one of the many ways to

print out a dynamic value in between

keep in mind you cannot use an

uninitiali­zed variable in Java so if you

the code will fail with the error

message variable age might not have been

instead of declaring and initializi­ng

the variable in different lines you can

after the name of the variable put an

assignment operator followed by your

now if you try to run the code again

you can change the value of a variable

as many times as you want so if you set

the value of the age variable to 28

instead of 27 just before printing it

out you will see that the value has

although you can assign new values to

the variable multiple times you cannot

declare the same variable twice so if

and try to run the code the code will

with the error message variable age is

if you look closely you will see two

different sets of curly braces in this

code the first set marks the start and

end of the hello world class the second

set is inside the class and marks the

start and end of the main method

code inside a set of curly braces is

since the main method is inside the

hello world class any variable you

declare inside the method will be only

these are local variables however you

can also declare variables outside the

method like here in the hello world

if you do that the variable will be

available within the entire class to use

this variable inside the main method you

will have to declare it as a static

we will discuss the reason behind this

in a later lesson for now just remember

that is static method can only work with

moving out the Declaratio­n of the age

variable and marking it as a static has

not made any difference whatsoever but

if you remove the value of the variable

and attempt to rerun the program

you will see the program runs without

any issues this time and prints out 0 as

this is because whenever you declare a

variable in the class level the Java

compiler will assign a default value to

it for numbers it's always zero now

another thing that I'd like to show you

if you redeclare the age variable inside

there will be no problem whatsoever

because the initial Declaratio­n of the

age variable is not local to the main

so as long as you do not re-declare a

variable within the same code block you

when it comes to naming your variables

you can name them anything as long as

the names don't start with a number and

don't have any spaces in them there are

also around 50 words reserved by Java

itself as keywords and you cannot use

any of them either you can start a

variable name with a dollar sign or an

underscore but excessive usage of these

signs can make your code unreadable in

case of multi-word names always follow

camel casing when naming your variables

if you want to learn about different

programmin­g naming convention­s I leave

the link to this article in the

descriptio­n finally avoid naming your

variables using single letters

now that you know about variables we

will discuss the different types of data

keep in mind I have reorganize­d the

source file to better reflect what I

will be talking about at a high level

there are two types of data in Java

there are the Primitive types and the

non-primit­ive or reference types

primitive types store values for example

int is a primitive type and it stores an

integer value a reference type on the

other hand stores the reference to a

memory location where a dynamic object

is being stored we will discuss

there are eight primitive data types in

Java six out of those eight types deals

with different types of numbers first

there are the bytes these are small

numbers within the range of -128 to 127.

then there are the shorts with a much

larger range than bytes and the integers

with an even larger range if you ever

need to store a value so large that it

doesn't fit in an INT you can use the

long type by default any number with no

decimal point is treated as an integer

by the compiler to let the compiler know

that a number is actually a long you

have to append the letter L at the end

of the number you can also use a small l

in instead of the capital L if you want

for numbers with decimal points in them

there are double and Float types doubles

are double Precision 64-bit floating

Point numbers with a very long range

floats on the other hand are single

position 32-bit floating Point numbers

with a smaller range by default any

number with a decimal point is treated

as a double by the compiler to let the

compiler know that a number is actually

a float you have to append the letter if

at the end of the number like the lungs

you can use a small If instead of the

Boolean data type can have only two

values true or false at the moment usage

of a data type that can only hold true

or false as values may not seem that

useful to you but once you learn about

conditiona­l statements you will see

finally the character type can hold any

valid Unicode character the Unicode is

kept sequence for the copyright symbol

is backslash u00 A9 so if you store this

value in a car variable and print it out

on the console like this we have

that the copyright symbol has been

printed on the console instead of the

value we have saved of course you can

also save any standard character from

your keyboard instead of this kind of

Unicode subsequenc­es for example if we

remove the name Copyright symbol and

change it to something like percent

and replace these Unicode Escape

character with the percent sign

and update our code accordingl­y

the percentage symbol printed out on

Console instead of the copyright symbol

now for the most part when working with

the in-type should suffice and for

numbers with decimal points the double

type should suffice but you should also

although you cannot store one type of

data inside another type of variable

conversion between the different types

is absolutely possible type conversion

in Java can be either implicit or

explicit when the compiler converts a

for example an integer to a larger one

like a double automatica­lly it's known

as an implicit or narrowing type

first get rid of all the old code in our

then Begin by declaring a new integer

you can call call it anything

and for the value of the double type

is essentiall­y doing is first taking an

integer with a value of Phi and then

taking a double and assigning number one

let's try to print it out using the

so as you can see the compiler has

successful­ly converted the integer to a

this is because a w is larger than an

integer but what will happen if you try

to do the reverse let's try out

this time start with a double

the program immediatel­y fails saying

incompatib­le types possible lossy

what the compiler is saying that an

integer to double con conversion is not

possible automatica­lly although

conversion from an in to a double is not

possible automatica­lly you can still do

it explicitly by letting the compiler

know that you want this to happen

the cast operator can be of help here

first inside a set of parenthese­s right

end this will tell the compiler that you

want to convert this double to an it

let's try to run the program once again

and this time the program works without

any issues but you have lost the point

eight part after 5. if you are doing

explicit type conversion in Java be

extremely careful whether the type you

are converting to will be able to hold

the entire value or not in this case I

knew that an integer will never be able

to hold the entire 5.8 value and I will

lose the second part but I went with it

so as long as you know what you are

doing you should be all right but at any

given moment if you perform an explicit

conversion and lose a bit of data

accidental­ly the results can be

catastroph­ic now that you know about

variables and the different types of

data you can work with in Java you will

have to learn about operators keep in

mind I have made some changes to our

code to better explain our topic in hand

and since our code has become much

longer than before I suggest that you go

and change the default layout from

stacked to side by side and then hit the

reset layout button to apply the new

this will give you a lot of vertical

space and make the code easier to read

operators in Java or programmin­g in

general are certain symbols that tell

the compiler to perform certain

operations such as arithmetic relational

or logical operations although there are

six types of operators in Java I will

only discuss four bitwise operator are a

little bit more complex than the other

ones and I don't think they fit well in

a beginner's course like this we will

begin our discussion with arithmetic

operators arithmetic operators are the

ones that you can use to perform

arithmetic operations such as addition

subtractio­n multiplica­tion or division

or so on there are five arithmetic

operators in Java and these are the

addition operator the subtractio­n

operator the multiplica­tion operator the

division operator and the remainder

operator the remainder operator is also

known as modulo or modulus operator

addition subtractio­n multiplica­tion and

division these four are pretty

self-expla­natory you can have a look at

and you should be able to understand

what they do and how they do it if you

have used a calculator in real life the

arithmetic operators in programmin­g work

similarly in our code we have two

integer numbers number one and number

two with the values 12 and 6

respective­ly so if you add number one

and number two together the result will

be 18. if you subtract number two from

number one the result will be six if you

multiply number one with number two the

result will be 72 and finally if you

divide number one by number two the

result will be two we will talk about

the remainder or modulo operator later

the addition and multiplica­tion

operations in this code are pretty

simple but the subtractio­n and division

operation needs some more discussion so

we'll comment out the division code

and the remainder code and focus solely

on the subtractio­n part as you can see

the value of number one is 12 and number

two is six which means the number one is

subtractio­n operator comes out as

positive but if we change the order of

the operation here so if we make number

two the first operand and number one the

that the result of the operation changes

from 6 to -6 again if you have used

calculator cngl live before you should

already be aware of this situation

now the division operation since

dividing 12 by 6 yields the result 2

this operation is perfectly fine but if

we change 6 with something like

then the result will not be a whole

number as you can see according to this

program the result will be 2 but if we

perform the same operation in a

calculator or by hand we will know that

the result of this operation should have

been 2.4 now this happens because if you

divide an integer with another integer

the result will always be an integer so

let's try by changing this integer type

as you can see this time the result is

2.4 but what happens if we divide a

again the result is 2.4 and if we change

the first operand to an end and the

second to a double the result will still

be 2.4 which means if you divide an

integer by another integer the result

will always be an integer but if you

divide a double or float by an integer

or divide an integer by a double or

float the result will always be another

now let's get rid of our division code

as well and focus solely on the

remainder or the modulus operation

now for this example I would like to go

back to our original verus which are 12

and I'd like to go back to integer

let's run the program and see what is

compiling a program may take some time

but we just need to be patient here

so as you can see the result of this

first we need to understand what is a

remainder now you may or may not already

know that a reminder is the value that

remains after you have divided a number

with another one so if you divide 12 by

6 the result will be 2 and there will be

nothing left you can always divide a 12

but if I change 6 to something like

and run the program once again

as you can see the value has changed

from 0 to 4 this is because if you try

to divide 12 by 8 there will always be 4

you have already seen examples of the

assignment operators in previous lessons

it's pretty simple you can use the equal

sign to assign a value to any variable

in your code but you can also combine

the assignment operator with the five

arithmetic operators you just learned

here we have a integer with a value of

12. now if I tell you that you will have

to add 5 with this value and Save in the

now the output of number should be 17

very simple but instead of doing this in

such a verbose manner you can do it far

let's just remove the second part here

and instead of using the assignment

then the assignment operator and then

this small line of code is actually

equivalent to number equals number

let's comment this out and see if this

gives the same result as before or not

so you can use all the five arithmetic

operators similarly say for example if

you want to take out 6 from 12 you can

do so by saying number minus equals 6.

and this will turn the value of number

there you can also do modulus operation

the result of this operation is 0

because when you divide 12 by 2 there

nothing left I hope you got the idea of

using assignment operator with all the

five arithmetic operators and I would

suggest that you try out usage of the

other ones like the multiplica­tion sign

and the division sign with the

assignment Operator by yourself and see

how the result varies from time to time

so far in this course you have learned

about the arithmetic operators and the

assignment operators the arithmetic

operators usually lets you perform

different types of arithmetic operations

on your numbers and the assignment

operator usually lets you assign

different kinds of value to variables

relational operators on the other hand

usually check the relation among

multiple operands by relation what I

mean is for example in this code we have

two integer numbers number one and

number two with the values 12 and 15

respective­ly now you may want to know

whether number one or number two is

equal to each other or maybe number one

is greater than number two or maybe

number one is less than number two or

not these are the relation between these

there are six types of relational

operators the first one is the equality

now keep in mind each relational

operator in Java or in other programmin­g

languages as well usually returns true

or false as a result of an operation for

example on line 7 I have written

system.out­.printelle­nt number one equals

equals number two the usage of this

double equal sign here is the equality

since the value of number 1 and number 2

is not equal the output will be false

which is correct in this case now you

may also want to check whether number

one is different from number two or not

for that you can use the not equal to

operator instead of putting two equal

signs side by side you will have to put

an exclamatio­n sign followed by an equal

now if I run the code again you will see

that the second operation gives us a

because indeed number one is not equal

then you can also use the greater than

operator to check whether number one is

greater than number two or not since 12

is smaller than 15 the output of this

there you go there is also the opposite

of the greater than operator which is

the less than operator and this

operation in this case will give us true

because number one is actually smaller

finally there are the greater than or

the less than or equal operator now the

greater than or equal operator will give

us true only if number one is greater

than number 2 or equal to number two the

less than or equal to operator on the

other hand will give us true only and

only if number one is less than number

since number one is actually less than

number two the greater than or equal

operation will give us false and the

less than or equal operation will give

us the result true now the usage of

these relational operators may not seem

uh that much fun to you at the moment

but once you start working with things

like relational statements you will

start to understand how important these

operators are The Logical operators in

Java or in programmin­g in general lets

you make logical decision based on

multiple conditions for example imagine

you are writing a program that can only

be used by people within the age limit

of 18 years old to 40 years old here we

have an integer number with a value of

25. now we will have to make two checks

first we will have to check whether age

is greater than or equal to 18 or not

and then we will have to check whether

age is less than or equal to 40 or not

so you have already learned about the

greater than or equal and less than or

equal operators in the previous lesson

here I will teach you how you can

combine these two operators using a

logical and operator to make a connected

decision okay so let's write system dot

out dot print Ln because we want to

print out the result of our operation

and start with the graded then or equal

operation age is greater than or equal

then you will have to put double M

person sign and this is the logical and

age is less than or equal to 40.

let's run the code and see what the

as you can see the output is true here

let me explain the logical and operator

in Java or in other programmin­g

in this way if the left side of the

logical and operator and the right side

of the logical and operator yields true

as a result then the whole operation

here the value of age is 25 which is

larger than 18 which means the left side

and it's also less than 40 which means

the right side is also true that's why

the result of this end operation will be

but if you change this value to maybe

something like 45 which is clearly over

40 years old and run the program once

you will see that the output becomes

although the left side is true the right

so in case of a logical and operator

both side of the operator has to be true

I apart from The Logical and operator

there is also a logical or operator okay

let's imagine another scenario

maybe you are writing a program for your

and to be able to borrow books from the

a person either has to be a student of

your school or a member of the library

so we can have two booleans here

which is false maybe this person is not

member is equals true maybe he is a

now to check whether this person is a

student or is a library member you can

use the logical or operator like this

and first we will check if this is a

or unlike the logical and operator you

have to use two pipe characters to

express the logical or operator and then

I hope you remember that in order for

the operation to be true in case of a

logical and operation both sides of the

operator had to be true but in case of

the or operation if either side of the

operator is true the entire operation

so as you can see although easy student

is false given is Library member is true

the operation gives us the result true

so if if you turn both of these booleans

and the only case when you will get a

is if both of these booleans are false

and finally there is another type of

logical operator in Java which is the

the not operator in programmin­g usually

a Boolean value for example here

the value of the easy student Boolean is

clearly false right if if you run the

program it will surely print out false

if we put a not operator in front of

this this this exclamatio­n sign is

actually the not operator and run the

you will see that it it turns out as

true so instead of using the not

operator over a single Boolean value you

can actually reverse the value of an

entire and or or a person in Java like

this let's go back a few steps

and I I hope you remember that in this

case we got the result false because

both of these booleans are false

now if you put a not operator in front

of the Esky student Boolean this will be

so now if I run the program the result

of the entire operation will be true

yes there you go the different types of

operators that you have learned about so

far easily work with multiple operands

except the not operator it usually works

on a single value or variable at a time

now these kind of operators that usually

work with a single operand is usually

unary operators apart from the not

operator there are also two more

that are unary in nature and very

commonly used in programmin­g these are

the increment operator and decrement

assume that you are trying to make a

game where you have to store the score

of the player and the number of turns

left now you can store these values in

two different integer numbers maybe

now whenever you have to increase the

value of score by 1 you can do so by

saying score plus equals one you have

already learned about the usage of the

arithmetic operators along with the

assignment operator in previous lessons

well this is one way to do this using

this method you can actually add any

but since here in this code you will

only increase the score by one

well you may think that what kind of

gain that is that gives you one in every

term well that's just for the example

so putting two double plus signs after

an integer or maybe float or double or

any number kind out there will increase

its value by one similarly you can put

2 minus signs to decrease or decrement

the value of a number time now if we

print out the values of these two

and the value of turns is now 9. so this

is pretty simple incrementi­ng and

decrementi­ng values there is nothing

fancy until I I make it a bit complex

let me show you something let's get rid

of all this code and declare a new

now if I say system dot out dot print Ln

you may think that this will print out

EU increment 55 by 1 and it becomes 56

well let's see if if that's true or not

seems like that the value has not

incremente­d at all okay let's make a

this time the value has changed but

at line 5 where you have used the plus

plus or the increment operator the value

remained unchanged but on line 6 while

you have haven't used any uh operator at

all the value seems to be incremente­d or

you see when the compiler reads your

code it usually goes from left to right

system.out­.println and sees the number

variable here it immediatel­y prints out

so at that point the value of number

an increment operator here and it goes

like Oh that means I have to increase

then the compiler increases the value of

number 256 and keeps that in memory so

if you ever print out the value of

number later on it will actually print

now this is same for the minus minus

sign or the decrement operator

initially the value will be 55 even

though the value has changed in the

memory and on the second pretty

so far I have showed you only one way of

writing the increment or decrement

operator instead of writing it at the

end you can also put it in front like

and let's see what output we get in this

as you can see this time we are getting

56 because when the compiler reads your

code from left to right it goes like

system.out­.printelli­n and it immediatel­y

encounters the increment operator and

then it sees the number and goes like

okay so I have to increase the value of

number and then print it out so it

prints out 56 on line 5 and on line 6 as

same goes for the decrement operator

54 and 54. so this is something that you

should be aware of when using the

increment or decrement operator inside

other statements like in this case the

if you are just incrementi­ng or

decrementi­ng the number outside of

anything like this method called like

then you shouldn't have any problem at

see so if you ever get like unexpected

values after using the incrementa­l

decrement operator in your program just

make sure that you are using it

correctly or you are using it in the

right place I hope that you remember in

a previous lesson I have taught you

about the character type it is one of

the Primitive types in Java and you can

store any Unicode character in it like

in this example I have stored the

percentage sign in a character variable

called the percent sign and I have

printed out the character on my console

now the character type is good and

everything but if you want to store

multiple characters together for example

your name or a sentence you cannot use a

for this type of scenarios we have

string in Java there are multiple ways

let's see the literal way first

and then name of the string in this case

so this is my name you can put any

string right here and then you can print

to declare a string in Java is by using

the new keywords the new keyword in Java

can be used to create new objects from

classes now we have not discussed

classes at all in this course yet but we

will get into classes and objects and

object rendered programmin­g later on for

now just remember that the new keyword

can be used to create a new object from

Now to create a string using the new

keyword you will have to write string

like if you run the program there should

be no change whatsoever because

essentiall­y declaring the string this

way or that way it doesn't make any uh

visible changes to the program but there

is a slight difference in in these two

techniques now the jvm or the Java

virtual machine usually uses a portion

of your computer's memory to store

strings now this little portion of

memory is usually called the string pull

now whenever you create a new string in

Java will first check whether this

string Farhan has injury already exists

if it does then the jvm will simply

reuse that previously string with a new

but in case of the new keyword the gvm

will create a new object regardless of

whether this value already exists in the

I think this can be demonstrat­ed with an

for this I will create four strings

literal E string 1 equals to A B C

and I'll create another literally string

with the same value but different name

now I will create two object string

I mean don't get me wrong these strings

are actually same but I am just naming

them as literally string and object D

so I'll make a copy of this string

change its name to object string 2 with

now if I compare these four strings with

equals equals literal string two

and I'll make a copy of this line

and use object string instead of literal

let's make this wider so that the code

becomes easier to read and now if you if

as you can see when declaring a new

string using the literal format

since the value ABC was already present

in the string pool that jvm actually

reused the older value with literally

shrink to but when using the new keyword

even though the same value has been

assigned to the two string variables

they are not same you have already

learned that the W equals sign checks

for the two objects are same or not and

in this case the literally strings are

actually same since they are using the

and the objective strings are different

entities because they are not reusing

the same values from the pool

now depending on your Necessitie­s you

may go with either of these techniques

but I'd suggest that you go with the

technique if there is no problem with

that because this will not only make

your code easier to read there is no new

or there is no duplicate is string

written in the code but also it will let

the compiler optimize your code a little

but the strings in Java are not

primitive types these are object types

and the strings are literally one of the

most powerful types in Java you will use

strings a lot throughout your entire

programmin­g carrier and there are a lot

of methods that we can use with this

Stream So now I will demonstrat­e a few

of those essential method that you can

use on strings and do fancy things with

this depending on the type of software

you are working on you may or may not

have to work a lot with string

now let me explain this topic with an

you go back to the Stacked layout from

side by side because now our code will

get a lot longer sideways and not

okay let's begin by removing everything

and writing a single system Dot

out dot print as an statement and in

here we will write a pretty long

here so you're getting the entire line

now we can take out a bunch of stuff

from this line such as my name

now to use these variables inside this

string you can use the plus sign you you

may have already seen example of using

the plus sign to like slotting Dynamic

you can do the same here so I'll get rid

of farhanasan Chaudhary and in the

the first string starts here and ends

the second one is starts here and ends

and in between the two strings I put my

next I can take out the country name as

so I will separate the strings put two

plus signs and put country in here

plus signs and the variable name

okay let's save the code cross our

yeah as you can see the output is fine

but I hope you are getting a sense of

how complicate­d this string can get once

you start adding more variable sites

such as if I add my company name the

uh company girls let's say free code

so I can change it to I work or

now you can put plus and a DOT

yeah works just fine so the point I'm

trying to get through is the fact that

Azure string grows and you start to use

more and more variables in it using the

plus sign to concatenat­e strings or add

them together becomes really clumsy

there is a better way to do this

and that's formatting your restraints

so let's declare another string called

formatted string equals then we will

and I work or modulus s so once we have

written this line we will say comma

so my name is modulus s so this modulus

or modulus D these characters are called

format specifier so when the Java

compiler comes and reads your line like

this my name is modulus is the compiler

knows that there will be a certain

string here and when it reads I am

modulus D years old the compiler will

know that there will be an integer

number here but the compiler doesn't

know yet what is string or what integer

value will replace this format

so once you have finished writing your

string along with the format is

specifiers you will have to put a comma

and then put in the variables in the

same order of the formatting specifiers

for example we have my name is modulus s

and we want to replace this part with a

name variable so we will put name

and then I am from modulus s and we want

to replace this format specifier with

comma then we have modulus D which we

finally we have one more modulus s that

we want to replace with the company name

there you go now we have a formatted

string so instead of writing this a long

string with plus signs and variable

names and what not in it we can just

and as you can see it works out just

so far you have seen the format

specifiers or strings and integers there

are also certain formative specifiers

for floating Point numbers and booleans

so the format is specifier for a

floating Point number B it a float or a

so if I put in a double here like

my GPA is modulus F and we can replace

the format is specifier for a character

is modulus C and A Boolean is modulus B

now I can't think of any fun example to

demonstrat­e modulus B and modulus C

percent sign equals to put the percent

and I can say I have attended

excellent and after the GPA I can just

use a comma and put percent sign here

equals false now I'm not reading the

truth I I haven't added 100 of my

classes and my GPA is also not 3.8

am I telling the truth yeah right these

and then am I telling the truths yeah

that's a really horrible name to be

excellent my name is Farhan Hassan

Chaudhary I'm from Bangladesh I am 26

years old I work for free code Camp my

GPS 3.8 I have attended 100 of my

University classes these are all false

so as you can see the string dot format

method returns a formatted string by

replacing all the specified format

specifiers with your given values now

instead of saving this formatted string

in a separate variable like I have done

here you can actually just copy the

and paste it inside the println call

although it works and you can do this if

you want but I would not suggest doing

there is something called the printf

function that you will learn later on in

this course that actually lets you uh

use the formative specifiers right in

so for now I would suggest that you save

your formatted string in a different

variable and then print that out using

println or use that however you see fit

so remember the format is specifier for

for an integer number also for shorts

for floating Point numbers both floats

while working with strings in Java it's

really common to check the length of a

string or you may want to check whether

a string is empty or not like a lot of

things in Java doing these two tasks is

let's start with a single string okay

I have to check the length of this

first the name of the string which is

the length is a method that remains

inside every string that you create in

as you can see the length of the string

is 22 which means there are 22

characters in the entire name including

now you can also check whether a string

to do so you can just write the name of

the string which is name in this case

empty this is another method that

returns either true or false if the

string is not empty then it will return

false and if it's empty then it will

return true let's run the code and the

output in this case should be false

since the string actually contains some

characters in it now if I get rid of the

name inside the string and just

put two quotation marks with nothing in

between them and run the code again this

time the string will be treated as an

empty string and the output will be true

now the length and is empty methods can

be pretty useful in certain scenarios so

I would suggest that you remember them

and practice their usage as you go along

you can also convert strings from

lowercase to uppercase or uppercase to

lowercase in Java to do so first you

then to convert this string to uppercase

you just need to write the name of this

string which in this case is same then a

you will see that the name has become

uppercase however you may think that

these two uppercase method has actually

changed the original string which is not

so if we add another println here

printing out the original name you will

you can also convert the name to lower

and this will convert the entire string

there you go in a previous lesson I have

taught you two ways to declare new

strings in Java there was the literal

way that usually reuses the string value

if it's found in the string pool and

then there was the usage of the new

keyword and I hope that you also

remember that when you created a string

using the new keyword like this

difficult to new string and the value

and try to compare them using the equals

equals operator or the equality operator

stem dot out dot print Ln is string 1 is

that the output of this operation

this is because even though the value of

the two string is same these are not the

same object and the equality operator

the object on the left side is same as

the object on the right side or the

object on the right side is same as the

object on the left side now to compare

strings you will have to instead use the

equals method so we'll first write the

let's run the program once again

and this time the output is true

however if you change the second value

sure the output will be false this time

but there can be cases where you want to

check whether a string is equal to

another string or not ignoring their

so for those scenarios you can use the

case method instead of the regular

so as you can see even though the two

strings have different casing the output

is still true you can also replace a

part of a string in Java to do so first

and then say for example we would like

to replace the word blue with the red

uh string which is the name of our

string right now and then replace

you'd like to replace the word blue

then run the program and see what the

as you can see the word blue has indeed

been replaced with red now you may think

that the replace method changes the

there you go what it actually does is it

replaces the white blue with red in the

string and Returns the updated string as

so instead of putting it directly into

the println method you can also do

and then put updated string inside the

so this will give us the same result as

you may not always want to replace a

substring within a string but you may

want to check whether a string contains

a certain word or substring or not

you can do so in Java as follows

so we will use our previous string which

says the sky is blue and we'll check

whether this string contains the word

sky or not to do so you will say string

which is the name of our string here

and you will need to pass the string

that you want to check for to the

contains method in this case it's sky

since the string contains the word Sky

the output is true but if you put

something that is not present within the

back when I was learning to code for the

first time one of the things that I

learned and it gave me a sense of

achievemen­t was being able to take input

from the user so far in this course you

have learned about different types of

data operators and outputting text on

the console in this lesson I will show

you how you can take different types of

inputs from the user as well as print

out text on the console in some other

formats if you are familiar with

programmin­g languages like python where

taking input is a matter of a single

line you may be disappoint­ed to learn

that in Java you have to write quite a

bit of code to take an input from the

user now the first thing that you need

to take input from the user is something

called an scanner object now scanner is

one of the classes in Java and you can

use the new keyword to create a new

so you begin by writing scanner

since the type of the object will be

scanner and you can name it anything but

I prefer naming it something simple like

and you will have to let it know from

where you are getting the input so since

you will get the input from the console

or The Terminal you will have to write

now this scanner class that you are

seeing here it doesn't exist in your

you will have to import it first so

before the first line where you declare

the class you will have to write import

now you may be seeing this import

statement for the first time here but

it's nothing complicate­d there will be

scenarios where a certain class will not

be a part of your current program or

your current class and you will have to

so the Java language comes with a lot of

such classes that can be really useful

in different scenarios this scanner

so once you have defined the new scanner

object you can take input from the user

so first I would like to speed out

something informativ­e on the screen like

and then I'll in the line here and I

now the scanner dot next line method can

be used to take strings as input from

you will have to save this input

somewhere though so you can say

a string name equals scanner dot next

just let's print out the name for now

okay let's run the program and and see

okay as you can see there is this

quickly line under scanner and if you

hover over it it says resource link

scanner is never closed well what it

essentiall­y says is once you are done

with the scanner you will have to close

it it's like an Open Door so if you if

you do not close it it will be active on

the memory so you will have to go like

scanner Dot close and this quickly line

yeah now the programmin­g's fine let's

enter and yeah it prints out my name

inputting my name after the prompt like

what is your name then inputting my name

in the next line may look a bit little

bit weird so instead of using the

println method what we can use here is

the print method so the print method is

actually similar to the println method

but the main difference is that it

doesn't have a new line character at the

so as you can see now the text prompt is

right after the question marks

yeah enter and yeah that's nice

now in case of a println method there is

usually a new line character at the end

so this causes the text cursor to go to

let's run the code to see how it changes

yeah as you can see now it mimics the

now apart from the print method there is

another useful cousin of this print

alone method called the printf

in a previous lesson I have showed you

how you can create formatted strings

using different types of format

specifiers and I also told you that

there is a variation of the print Ln

method that lets you use this format

specifiers right within the print method

okay that's that's the printf method or

print formatted now instead of just

printing out the name like this we can

and we would like to replace the modulus

with the name so we put name I hope you

remember all the different affirmativ­e

specifiers that you have already learned

about if not you can just go back and

re-watch that lesson let's run the

treats me and also asks how am I okay

so you have learned that the next line

method usually gives back a string from

the user but you can also ask for

specific data types such as maybe an

so to do so let's modify the next print

and then we would say int age equals to

and we would like to print out

yeah and sorry not printed on print f

modulus D is an excellent age to start

like any age is like accidental learn

and we will put age here so this modulus

D part will eventually be replaced by

what is your name okay my name is Farhan

how old are you 26 maybe yeah

26 is an excellent age to start

okay now so far so good like the next

line method and next int method there

are also methods for double like scanner

dot next Double and next float and all

those different types that you can think

but one thing that I would like to draw

your attention to and something that

catches a lot of uh Java beginners or

card is a little quirk so as you can see

I am asking for the name using the next

line method then I'm asking for the age

using the next int method and it works

out just fine but let me show you what

happens if I try to use another next

line method after this next int method

so if I say system dot out dot print Ln

okay let's just reuse this line okay

some excellent cage just start

string language equals to scanner dot

sorry I I missed the language here

now look carefully what happens when I

run the program okay so I run the

so first it asks for my name Chase

and then it skips the last prompt where

I'm asking about the programmin­g

language preference and just insta

program abruptly and the worst part is

there is no error or no failure at all

which can help you to debug this problem

well this is something uh this has to do

with the way the next end and the next

line method works so let me explain

so when you are saying a string name

equals to scanner dot next line and I'm

inputting my name then I'm pressing

the next line method is actually taking

the entire name along with my enter or

my new line character at the end or the

character when I press enter that goes

but when it comes to the next int method

it only takes the number or 26 as an

input and leaves the new line character

or carriage return in the buffer in the

input buffer so what happens is when I

say at 26 and then I press enter

this part will be consumed by this

method next end but the enter will be

so when the second next line call comes

it sees that there is already an enter

in the input buffer and mistakes it as a

so it assumes that the user has already

inputted the text they wanted to input

insta call right there okay I hope it

now there are multiple ways to like deal

one of the ways is whenever you put a

next in call or next Double call or next

float call whatever it is except next

an extra scanner dot next line here so

this just like cleans up the input

so this next line method eats up the

by the next int and cleans the input

buffer so if we run the program now

what language do you prefer well Java

so this is something that you should

keep in mind that whenever you are using

a next ink call anything but a next line

call and you want to put another next

line call after that like we have here

an extent and the next line you will

have to put an extra scanner dot next

line call just to clean up the input

buffer just to get get rid of that uh

leftover Enterprise okay otherwise your

program May skip the next call okay

deal with this situation is instead of

using methods like next end or next

float you can just use next line for

taking all the inputs and then once you

have taken an input you can just

like convert it to something else okay

for example uh instead of using the next

ink if we use the next line method here

so what we can do is we can say integer

and then put the scanner dot next line

and let's run the program and see what

um Java yeah it works out just fine and

we do not have to use any extra scanner

objects as well now if you had like

instead of int you may have like uh

double here you can do so a double say

for example if we uh want to take the

GPA of the user equals to to be the

and then scanner Dot next one

and this will work out too okay so uh

all of the first method that we have in

these classes like integer.pa­rsing

double dot purse double we can use all

of this now you may think that how would

I know uh which method to use when you

are trying to purse a number from a

string well uh one way that I suggest

everyone is you can just Google it uh

saying how to purse integer from a

string in Java or maybe how to purse a

double from a string in Java and so on

or this is something that I would leave

up to you to figure out because this is

something that you do not learn in

okay so I hope you have learned about

taking inputs from the user the main

thing you need is a scanner object and

you will have to let it know from where

uh you can also take input from a file

and some other places but those are a

for what you know at the moment and you

will also have to remember to import the

scanner class first otherwise the code

will just fail okay if I comment this

out and run the code you will see the

program simply fails to find the scanner

it says cannot find symbol so make sure

that you have imported the class at the

and the rest is pretty simple I guess so

now that you have learned about taking

input from the user and outputting text

on Console using printf print and

uh in the next lessons we will learn

about something called the conditiona­l

statements and we'll make a very simple

calculator project that will just show

with what you have already learned

now you have already learned about The

Logical operators and taking input from

user to all the most important things in

programmin­g in this lesson I will teach

you something called conditiona­lly

statements that lets you make logical

decision based on some conditions and

Branch out your code in different ways

for example we will make a calculator in

this lesson and we will let the user

multiplica­tion and division operations

so first we will need a scanner of

okay yeah so you need to close the

scanner as well okay let's begin with a

equals to scanner dot next Double

we need to output something on this

we'll put enter the second number

and let's just output the numbers to

make sure that the input is working fine

and then let's make a copy of this line

yeah looks like the input is working

now we'll need to ask the user what

operations they want to perform for that

and okay we will use print instead of

print alone and then we will have to

operation equals to scanner dot next

so as I have already told you that this

next Double calls will leave two next

line characters in the input buffer so

we will need to clear them out first so

let's just put this extra calls here

and once we have taken the string

then we can check what it is okay

so the if statements in Java or in

programmin­g in general lets you check uh

whether a certain value meets a certain

condition or not for our case we can say

then a set of parenthese­s operation

so if the user has written some as the

what you want to do is system dot out

Dot println and we will say not println

modulus D plus modulus T equals to

modulus D comma so we want to replace

the first modulus D with number

this should have been F actually since

you're working with double sir and not

number two finally number one plus

space them out in the line with the

let's check out our simple calculator

and see if we can do the summation

so the first input will be five you can

put anything you want the second number

what operation do you want to perform

yeah 5 plus 10 equals 15. now what

happens if I put anything but sum okay

the operation is equals to sum or not

if it returns true then the line inside

the if statement will be executed but

what happens if we input something else

maybe subtractio­n or sub you see nothing

happens so for situations where an if

statement fails to fulfill the condition

and we can print out system dot out Dot

modulus s is not a supported operation

and you can put a semicolon here and we

can say comma operation let's see how it

sub is not a supported operation

now I have already said that we will

Implement a summation subtractio­n

for that what we can do is we can put

and we can put another condition here so

change the plus sign with minus and also

minus then we'd want to close this Gap

so now what will happen the program will

ask for the first number then the second

number then ask for what kind of

operation the user wants to perform and

then first it will check if the

operation is equal to sum or not

if it's equal to sum then it will print

out the sum of the two numbers

if it's not the sum then the ladder will

whether the operation is equals to sub

or not if it's sub then it will perform

the subtractio­n operation and give out

the value and if the operation is not

sun and also not sub then it will go

into the else block and print out that

this is not a supported operation let's

Ty is larger than the first one

the value is negative similarly we can

just implement the multiplica­tion and

division operations so let's just do

and just copy this entire line

finally the division operation

is a little different operation equals

then first we will have to check

we put another if inside this lcf and

this is called a nested if block so we

cannot divide by zero because you just

cannot divide a number by zero and then

we'll perform the division inside

and we'll bring up the else block here

and now let's let's check out the

Division and multiplica­tion operations

a mul a multiplica­tion via 80. excellent

so we have already managed to create a

very simple calculator here capable of

Performing the basic arithmetic

now I'm not saying that this is the only

way to implement a calculator you can

actually uh find even much better ways

of making calculator­s but so far what

you have learned this is a pretty good

implementa­tion of all your knowledge

now when it comes to branching out your

code based on one or more conditions if

else's statements are pretty common but

this is not the only way of doing things

there is another statement called switch

case statement that can do the same

thing as a complicate­d if else ladder in

this lesson we will convert our

calculator applicatio­n to use a switch

case statement instead of ifills

statements now before we dive into our

code I would like to go to settings and

from stack to side by side because

as I'm seeing our code is becoming much

longer vertically and it's becoming

harder to read we can also make the

console smaller for now because we need

now we can retain most of our code from

our previous example we can keep the

scanner the inputs for number one and

number two the input for the operation

and the only thing that we need to get

rid of is the Ifill statements

now instead of removing the code

to write switch case statement in Java

you will have to begin by writing

and then within a set of parenthese­s you

will have to put the variable that you

so if you remember from our efels

statement we are testing out the value

of the operation variable and see

whether it matches one of the four

operations or not so inside the switch

then we will put a set of curly braces

now you may have already guessed from

the name of switch case statements that

there will be multiple cases inside a

now these cases are like this individual

if statements where you are checking the

value of the operation variable against

so in the first case of this statement

we will check whether the value of the

operation is some or not to do so you

and then the value you want to check

against which is sum in this case

and on the next line you can put the

so I will just copy the code from our

previous evil slider and put it here

let's run the code and see what happens

okay Enter the first number I

and put five into the second number 10

okay it says 15 which means it works now

try to put a value that is not defined

within the switches statement like sub

and as you can see just like the if

statement when you didn't have an ill

it doesn't print out anything at all

now in case of switch cases statements

you do not have else but you will have a

default guess which you can write as

and then you can just print out that

this is not a supportive operation

let's run the program and see what

okay savvy's not a supported operation

fine now so far this looks okay but let

you will see the program not only prints

out the summation of the two numbers but

it also prints out is not a supported

well the way switch cases are designed

that if one of the cases match then the

program will not only execute that case

but also the cases that comes after that

to stop the program from going through

all the cases here what you'll need to

so when the program comes and it sees

that the sum case has been matched it

will execute the logic here and then it

will encounter the break statement and

breakout of this entire switch case

statement okay and it will go directly

to scanner.cl­ose Let's test it out once

so as you can see it prints out the sum

and breaks the program right there

you can actually Define the other cases

subtractio­n logic from our previous efl

put it here put the break statement in

best okay so the third case would be the

we'll change the minus sign so if the

and finally the division case

now I hope that you remembered that we

also had a check to make sure that the

user is not trying to divide by zero

we will have to do that as well and for

that we do not have anything fancy we

will just need to rely on plain old if

else step map so we will write

number two is equals equals zero

then we would like to print out

else we would like to perform the

keep in mind that you should write the

break statement outside of both the if

and else block otherwise if you put the

break inside the if or the else then it

one of them are active but if you put it

out here no matter what happens in DC

fills block the break will always work

let's try it out and see if it works or

cannot divide by zero okay let's rerun

the program and check if the normal

division function works or not

yeah it works finally let's check the

now you can get rid of the commented out

now although e-fills statements and

switch cases statements are more or less

do the same thing in the context of Java

or in the context of other programmin­g

a switch case statement is actually

faster than an if else letter in Java so

if you can put your logic within a

switch case statement instead of a

really elaborate if else statement try

to do that so far in this course you

have only stored single values in single

variables but there is a way to put

multiple values within a single variable

now before I start working on arrays

you can get rid of more or less

everything in our code you can also get

now to declare a new array for example

if I want to declare an array of

characters and I want to store all the

vowels in English alphabets you can do

first you will have to type out the type

of the array which in this case is car

space then the name of the array which

then you will put an equal sign and new

car then you will put another set of

square braces and inside of these Square

braces you will have to put the length

of the array now we know that there are

five vowels in the English alphabet so

now we have an array of characters but

it's completely empty to insert a new

value to this array you will have to

and then an index of the array which in

then equals then the value you want to

now I have already told you that this

array is of 5 length which means it can

now these characters here can be stored

like a e i o u and each of this

character will have a number associated

with them this number is called the

now the first index of an array in Java

is always zero so by putting vowels and

0 inside a set of square braces you are

essentiall­y addressing the first place

then you put equals a and you fill it up

now the other spaces are still blank

and paste it to insert the other values

now you have completely filled this

array with the five vowels of English

you can also print out these individual

files using the same square brace syntax

and write system dot out Dot println and

put files and two inside Square braces

and print it out you will see I printed

yeah as you can see there is I

you can also print out an entire array

that's not as simple as printing out a

single character or number or a string

as you may have already guessed the

print printf or println function prints

out stuff on the console as strings

so before you can print out the array

you will have to convert it is string

import the arrays class like this import

and then inside the println method call

and in the name of the array which in

see we have printed out the entire array

now you can also print out an array

using Loops which you will learn in

later lessons for now just be informed

that there is also other ways of

printing out an entire array to the

so I have already mentioned that this

array has a length of 5. and since its

index count starts from 0 it will

obviously end at 4. now if you try to

put something in an index that doesn't

you will see that it fails with an

exception saying index 5 out of bounds

for length 5 which means for an array of

length 5 you cannot have an index 5.

and our code should be back to normal

now instead of declaring and defining

your arrays separately you can actually

declare and Define your array in one

to do so after you have written car

the pair of square braces and equal get

and put a set of curly braces here

then you can actually put the values

and in the line with the same colon

now you can also replace any of these

values from the array at any moment for

example if you want to replace the I

with any other character out there you

curly braces and the index of I is 0 1

put a semicolon at the end run the

and as you can see the eye has indeed

another thing that I forgot to mention

is the fact that when you are declaring

and defining your array in a single line

the array will actually infer its length

from the number of values you are

so since there are five values in the

definition the areas length will always

be 5. the light strings arrays in Java

are reference types and like strings

arrays also have a bunch of useful

methods in them for example if you ever

want to know about the length of an

array you can do so by saying that let's

and you can write the name of the array

I hope you remember that in case of a

string the length was actually a method

but in case of an array it's a property

and you can see the length of the array

a one of the most common tasks regarding

arrays that you may have to do again and

again within your programs is sorting an

right now we have ordered our files

array according to the order of the

letter as they come in the English

but if we change the order and kind of

randomize it so I will put e first

and I so a e i o u then it's totally out

now there is a method called sort within

the arrays class that you can use to

to do so you will have to write

and then put the name of the array

let's run the program and see

so turns out that the arrays.sor­t method

takes an array as its parameter and it

sorts the array in place so it actually

changes the original Source array by

default the arrays.sor­t method performs

the Sorting on the entire array so it

will begin from the first letter and go

through the entire array until it

reaches the last letter and sort them in

order but if you want to perform the

Sorting within a certain range of the

let's say for example if I want to keep

the e and i as they are right now and I

just want to sort the u a and o I can do

so so after I have put the array name

now to define the starting and ending

you can let's just Define to integer

starting index equals I'd like to start

I want to perform the Sorting until all

0 1 0 1 2 3 3 as the ending index

the O will be left out from the Sorting

because the ending index is usually not

inclusive in this case so I will have to

write 4. which means the Sorting will

take place from U to o n it will

Let's test it out after I have written

the name of the array I will put a comma

here and I'll put the starting index

the sort method has actually sorted aou

in order and did not touch e and I at

so this is one of the useful things that

you should know about sorting arrays in

Java apart from sorting an array you may

also want to search for a certain value

within an array okay so for example we

have e u a o i here and if you want to

look for o in the entire array you can

do so by using the arrays.bin­ary search

now one thing that you will have to

remember is that these areas.bina­ry

search method only works on sorted

arrays so if you have an array that is

not in order make sure you have sorted

it before performing the search

now to search for maybe o within this

and then I'll put the name of the array

that I want to perform the search on so

and then the key or the item I am

looking for so I'll write key

and I create a new character here uh key

equals to and I'm looking for what I'm

okay now this binary search method right

here returns an integer which is the

found item index equals to errors dot

binary search files excellent

now first I would like to print out the

and then I would like to print out

sorry I mistyped the name of the

variable here you know mistakes like

so in the array a e i o u o is at index

number three so we can verify that 0 1

2 and 3 o is at index number three like

the sort method that you learned about

just a few moments ago the arrays dot

binary search method can also take an

starting and an ending index

to use them first we will need to define

integers like int starting index I think

the search from one so I put one

then I will also create an ending index

equals to 4 because I want to perform

the search within the middle three

values and like the sort method

the ending index is not inclusive in

so once I have defined the two integer

numbers I will say binary search vowels

and finally the key I am looking for

now let's see if it works or not

okay so it says 3 which is correct in

this case as well I have found o at 0 1

now so far in this lesson I have shown

you a bunch of searches and all of them

has worked out fine but what will happen

if one of your searches failed to find

the value you're looking for for example

we do not have an X in the entire array

so if I get rid of the starting and

and look for an X within our array

you will see that the output is -6 now

instead of looking for an X if I look

so you may have already guessed that

depending on the item you are looking

for and if it doesn't exist within your

array then the output can differ

but one thing that's constant is if the

search fails you will always get a

negative output and if the search

succeeds you will get a positive output

and that positive number will be one of

the indexes from your array where the

item you are looking for exists now

there is a way to actually calculate

this value there is logic behind why the

output is sometimes 2 and sometimes six

but I will not get into that much

details in this course if you are

interested about learning this I will

leave the link to this article on free

code Camp under this video's descriptio­n

so you can follow that link and read

more about it now being able to sort an

unsorted array and look for any certain

item within an array is useful now

another small but useful thing that you

can do with arrays is that you can fill

for example we have five vowels listed

out of order within our vowels array

but maybe for some reason you want to

now you can do that by using the

arrays.fil­l method before that let's get

then put the name of the array that you

and the character or the value that you

want to fill the entire array with

let's run the code and see if it works

yeah as you can see the entire area has

now you can also have starting and

ending indices with this fill method

starting index equals let's start from

index equals to 4 this is the same drill

with the other methods as well the

ending index is never inclusive

so if you want to perform the field from

1 2 3 upon these three values make sure

to include the last one as well or the

item that's just after the one you want

to end the field action act okay now

arrays.fil­l comma vowels then we will

finally the value that you want to fill

okay so rs.2 string valves let's see if

yeah it does uh the E and I is untouched

and the U and O and A has been replaced

with x's I have already said that arrays

in Java are reference types and one of

the complexiti­es that we get with any

reference types out there is making

for example if we have an array of

integers this time just for changing our

same thing equals then inside of a pair

of curly braces I will put one two three

then I will create another array saying

copy of numbers which is an array

so ideally the copy of numbers array

should be a copy of the original numbers

let's see if that's true or not

let's make a copy of this line and put

let's run the code and see what happens

turns out I have made another typo here

so it seems like that the copy of

numbers array is indeed a copy of the

but I'm not convinced let's do another

let's make some changes to the original

numbers and I'll fill the original array

and then run the code let's see what

but this is unexpected isn't it

I have actually made some changes to the

source arrays and the changes have

somehow applied to the copy as well

but the reason for this is the fact that

arrays in Java are reference types and

when you use an assignment operator to

make a copy of an array or any other

it doesn't actually makes an entirely

new copy of the source material what it

does is it creates a new variable and

points that variable to the original

so although the second array has a

different name it's still pointing to

the same values so you can treat this

copy of numbers array as kind of an

alias for the original numbers area

so how do you make a copy of an array

correctly then now to copy an array

properly you will have to use

the arrays dot copy of method the method

takes the name of the original array as

its first argument and at the second

it asks for the length of the new array

so the length of the original array as

we can see is one two three four five

so you can count that by hand or you can

be a little bit clever and put numbers

dot length as the length for the new

let's run the code and see whether the

copy gets affected by the field call or

so as you can see that the original

Source material and the copy of it are

now two separate entities which we want

now instead of putting the same length

as the original array you can also make

the array larger or smaller let's say

so as you can see the first five

elements of the copied array are from

the original array and the rest of the

indexes has been filled with 0 which is

the default value for integers you can

and the copy array can hold only two

values while the original array could

and the search method you can also

Define the starting and ending indexes

for the areas.copy of method but for

that instead of using the copy off

method you will have to use copy of

range now inside this method you will

have to first give it the name of the

then and starting index and and ending

and just like before we will have to

Define this integers here and the

equals to Let's uh 0 1 let's start the

let's run the code and see what happens

the method has successful­ly copied 2 3

and 4 from The Source area now one thing

that you may have already noticed that

in case of the copy of range method you

do not need to use a link for the newly

so how can you increase the length of

well right now we are performing the

index number one to index number four

so if we put a larger value than the

original length of the array like

so as you can see the copy works out

fine the method copies 2 3 and 4 from

the original array also 5 and 10 fills

up the rest of the space with zeros

so although you cannot explicitly Define

a new length for your copied array you

can change the length of the new array

changing the ending index of the copy of

just like copying a reference type is

more complex than copying A Primitive

type comparing preference style is also

a bit complicate­d I hope you remember

from our lessons on string we couldn't

compare two strings simply using the

equal SQL signs we had to actually use

so it's kind of similar in case of

arrays say for example we have the

then we have a copy of the numbers array

and get rid of the field method

and try to compare our arrays using the

equality operator so we'll send numbers

let's run the code and see what happens

as you can see it says false but we know

for sure that the copy of numbers array

is an identical copy of the original

now to compare to identical arrays like

this or maybe two different arrays

what you'll have to do is you will have

then inside this method you'll have to

pass the two arrays copy of numbers

let's run the code and see what happens

yeah this time it comes out as true

since there is no such thing as casing

there is no equals ignore case method

for arrays like we had for strings in

programmin­g you may want to repeat a

certain set of instructio­ns again and

again for your projects you can do that

by using loops now there are four kinds

of Loops in Java and we will start our

discussion with a for Loop first I will

for a very simple for Loop in Java that

can print out the number from 1 to 10.

for this is the starting of our for Loop

then inside I will take an integer int

number equals to 1. now after the

a set of curly braces here and inside

this block of code I will write

we do not need the arrays class import

right now so we will get rid of that

and let's run the code and see what

happens then I will explain each line of

as you can see the program successful­ly

all the numbers from 1 to 10. so what's

going on here well every single for Loop

is the initializa­tion where we are

initializi­ng a certain variable in this

case an integer with the initial value

then there is a condition that we are

checking against so we are checking

whether the number is less than or equal

and if the number is less than or equal

to 10 we will print out the number so

this is the loop body system.out dot

println anything that you write inside

this set of curly braces will be the

then once we are done with the loop body

we will go to the third part here inside

the set of parenthese­s and this is

called the update and we will update the

every single for Loop will have four

parts there is the initializa­tion where

we initialize a variable with a value

then there is a condition that we will

check in every iteration there is the

loop body and then there is the object

so when this Loop runs for the first

time the value of number will be 1.

and this condition will be true since 1

is indeed less than 10. so the loop will

print out the value of number which in

then the loop will increase the value of

number by 1 and go back to the condition

part and check whether the updated value

is less than or equal to 10 or not well

so it will again go inside the loop body

and print out 2 on the console

so like this the loop will keep printing

out all this number until it reaches 10.

when the loop has printed out 10 on the

screen it will go back to the update

part and increase the value of number

from 10 to 11. and it will go back to

the condition once again and check

whether 11 is less than or equal to 10

in this case the condition will come out

as false and the loop will stop

the program ends here and we get all the

numbers between 1 to 10 printed out on

I hope that makes sense you can also use

a for Loop to Loop over an array

for example if we create an array here

then we can use this for Loop to Loop

over this array and print out each of

to do so we will need an integer and we

so we want to run this loop as long as

finally we will increase the value of

finally inside the println call we will

and then we will put the index here

so as you can see the program actually

brings out all the numbers from 2 to 10

and doesn't print out to 1 because

since the index count starts from 1

is its initial value it starts accessing

the array elements from index one so if

you change the value of index from 1 to

0 then you should get all the numbers

so what's happening here is you are

initializi­ng an integer with a value of

and then inside the condition part you

are checking whether the value of the

index is less than the length of the

numbers array or not if it's less than

the length of the numbers array then you

go inside the loop body and print out

whatever number is in the current index

so it starts from index 0 which means

then index 1 which is 2 then 3 4 5 6 and

you can also do some interestin­g things

within this Loop instead of printing out

you can add them all together and print

to do that what you will need is you

will need another integer here

initially the sum will be zero

and then inside the loop what we are

going to do is we will say sum plus

okay finally we'll move out this system

dot out Dot println outside of this Loop

and print the sum on the screen

let's see what happens when you run the

code I forgot the semicolon here yeah

so the sum of all the numbers from 1 to

10 is 55. now let me show you two more

interestin­g programs that you can write

the first one is that you can print out

multiplica­tion tables of any number

for that what we need is a number so we

will Begin by taking a new integer in

then inside the for Loop let's get rid

of all this code and rewrite the for

loop from scratch so we will say for

then another integer the multiplier we

will begin from one then if the

is less than 10 we will keep going

and we'll also increase the value of

then inside the loop body we can say

modulus D into modulus D is equals

then the second part would be the

and finally number into multiplier

now I hope you remember that the printf

method doesn't have any new line

so if you run the program at its current

as you can see it prints out the entire

multiplica­tion table in a single line

so what we can do is we can put a

backslash n at the end of the line which

will print out each row in a new line

now we can take it a bit further to the

let's get rid of the current code

and let's begin with the new for Loop

then inside the for Loop we will have a

nested for loop I hope you remember that

we have worked with nested if statements

in the past we can also nest for Loops

within each other so we can do 4

multiplier is less than 10 and

now inside the loop body we will say

modulus T into modulus T equals to

so the first thing would be the number

the nested for Loop is inside the outer

for Loop any variable declared within

the outer for Loop will be accessible

inside the nested folder but any

variable that you declare inside the

nested Loop such as this multiplier here

will not be visible to the Outer Loop so

we can send number so we will replace

the first modulus D with a number

and finally number into multiplier

okay just like before we have to add a

so as you can see now we have

multiplica­tion table for all the numbers

but if you would like to include 10 here

you can say less than or equal

yeah it works fine and I also just

noticed that we are missing again here

you can fix that by saying multiplier is

less than or equal to 10. right

so let me explain what happens here

first inside the outer for Loop you are

initializi­ng a number with one and you

are continuing to Loop until the value

of number exceeds 10 so less than or

and then inside the loop body you have

so first it comes and says okay number

is equals one it's less than 10 then it

goes inside the inner for Loop and it

sees that there is a multiplier with the

value of one multiplier­s value is less

than 10 then it goes inside the body

it prints out one into one equals one

and then it goes back to the update part

of the inner loop and it checks again

then it keeps looping within the inner

loop once the value of multiplier has

the inner loop breaks and the program

goes back to the outer loop it increases

the value of number by 1 which becomes 2

now and it goes inside the inner loop

again and prints out the multiplica­tion

table for two then it goes on to print

four five six seven eight nine and ten

so if you're having difficulty

decipherin­g this complicate­d code here I

would suggest that you write this code

yourself and use a notebook to

how these values changes in each

iteration okay so finally I would like

to show you an example of using an if

else statement within afford for example

if I tell you to print out all the odd

numbers from 1 to 50 you can do that by

using a for Loop and a single if else

number is less than or equals to 50.

number plus plus so this Loop will begin

then inside the loop body what we want

so if you divide a number by 2 and the

remainder is 1 it's pretty sure that

the number is an odd number we all know

so what we are doing is inside the for

Loop we are taking whatever the value of

number is we are dividing that by 2 and

checking if the remainder is one or not

that's what the modular operator is for

I hope you remember and if the number is

an odd number we will print it out and

if it is an even number we will skip

that let's run the code and see what

so as you can see we have successful­ly

printed out all the on odd numbers from

1 to 50 so 1 3 5 7 9 11 13 15 and it

there is another variant of the for Loop

that makes looping over collection­s such

now for that first we'll need an array

equals uh I'll just put the regular

to use this special type of for Loop you

then inside you will say int number this

type has to match with the type of the

and then you will put a colon here and

then you will put the name of the array

then inside the area body you can say

system dot out dot print Ln number

so as you can see the loop successful­ly

goes through the entire array and prints

out each element to the console now

What's Happening Here is uh you are

saying for every single integer number

in the numbers array you want to print

them out so instead of using an integer

as an index and accessing the elements

individual­ly you are kind of taking a

and extracting each value from the

numbers array and putting them in the

number variable on each iteration now

you can do anything that you could have

done in a regular for Loop such as if

you want the sum of all these numbers

and then system dot out Dot println

it's so make sure you are putting the

printerlan­d call outside of the loop

otherwise this will be printed every

single time the loop iterates let's run

the code and see what happens

there you go other than the for Loop

there is also the while loop and do

while loop in Java these are two

different kinds of Loops that can more

or less do the same thing as a for Loop

but the for Loops are a lot more common

in the wild than the while Loops now I

will show you two examples of using a

while and two while loop first let's

multiplica­tion table like we did in the

case of the for Loop but this time we

will use a while now first you will need

then you will need the multiplier

now to write a while loop you will have

multiplier is less than or equals 10

then inside the loop body you will say

modulus T into modulus T equals modulus

T since all of the variables are

integers in this case then you will put

then the multiplier finally the number

excellent then once you have printed out

the row in the multiplica­tion table you

let's run the code and see what happens

so here looks like the program works

just fine we have to just put a new line

character to make the output a bit more

now the main difference between a while

loop and a for Loop is the fact that the

while loop only has one component which

the condition in case of a for Loop we

had the initializa­tion we had the

condition we had the loop body and we

also had the update part but in this

case there is just the condition and of

course we have the loop body so you will

have to do the initializa­tions

outside of the loop and you will have to

the incrementa­tion of the multiplier or

maybe counter or whatever you are

so this is how a while loop looks like

Works similarly but in a different order

and also looks a bit different so in

case of a do while loop you will have to

then you will have the loop body

which in our case is these two lines we

want to print out the multiplica­tion

table once again and also increase the

and after the loop body you will say

multiplier is less than or equals 10.

let's comment out our old while loop

make our console bigger and run the code

output now the main difference between a

regular while loop and a two white Loop

is the fact that in this case first the

loop body will be executed and then the

condition will be checked whereas in

case of a while loop the condition gets

evaluated and then the loop body gets

executed so you will surely find usage

of both kind of Loops if you worked long

but I can say from experience that for

Loops are a lot more common than whites

let's just clean up our code before we

so far in this course you have learned

about only one way of putting a bunch of

values together and that is the arrays

but arrays have some limitation and the

biggest one of them is the fact that you

cannot resize an array the only way to

make an area larger or smaller than it

already is to copy it and change its

length during the copy but there is

another type and error list which is

like a dynamic array you can create an

arraylist you can put item in it or you

can take away items from it and it will

also adjust its length depending on how

now to use an error list in your code

you will have to first import the error

list class to do so you will have to

to create an array list you will have to

then you will have to put a less than

sign and inside you will have to write

the type of the data you want to store

now I know so far you have been only

seeing int and this is the first time

you are seeing something called an

integer used as a type I will explain

what this is but let's just keep on

typing and finish creating our new error

list okay so error list integer then

name of the error list which in this

that's it we now have an empty error

now what's this integer class here

I have taught you that data types such

Boolean these are all primitive types

but in Java you can also make them as

reference types using the wrapper

so this integer class share integer is

for the Primitive type INT in other

integer is the reference type form of

the regular inch type so just like

integer you also have double

and when you are creating an array list

you cannot use the Primitive in type you

have to use the integer wrapper class

since we have an in the error list in

our hand let's put some item in it

now to insert a new item in an error

list you cannot just use the old Curly

braces syntax rather you will have to

in this way you will have to write

then the value that you are trying to

add which in this case will be one

you can make a bunch of copies of this

now to print out an error list to the

console you will have to write system

numbers which is the name of our error

now the two string is a method that is

present in every single reference type

in Java and later on when you will learn

about object oriented programmin­g you

will also learn about creating your own

twisting methods within your custom

for now just remember that to print out

an error list you will have to write out

the name of the error list first and

let's run the code and see if it runs

so as you can see the error list looks

now you can also print out a single

from the arraylist if you want to

but for that you will have to use

the get method so you'll subdoc then get

then the git method actually takes an

which will be the index of the value you

like arrays error listers are also zero

based so the first index of an error

so the index of one in this case is 0

three and four so if you want to print

out three on the console you will have

to send numbers dot get and then two

beautiful we have three printed out on

I have already said that analysts are

Dynamic so you can add as many elements

as you want using the add method and you

can also remove elements from an error

and it will take a number which will be

the index of the element you are trying

to delete so if you want to remove 3

from our error list we will say numbers

then let's print out the entire error

list and see if she exists or not

yeah three has been successful­ly removed

but you can also remove items by value

so for example if I want to get rid of 4

instead of passing and primitive 4 if

you write 4 here this will be a

primitive integer Type 4 it will work as

a reference Type 4 like this integer

and then pass the Primitive type which

you will see that we have successful­ly

removed four from our error list now an

error list can store anything starting

from integers booleans characters

strings and your custom class objects

anything that you can think of we will

work with much more complex at least

in later lessons for now just let's get

hang of the basics okay now you can also

remove all the items from an error list

by saying the name of the earliest Dot

this will clear out the entire error

there you go so I have already showed

you how you can add new items to an

error list how you can get them remove

them clear an entire analyst now let me

show you how you can update an element

for that there is the set method

so you will type out the name of the

and you will have to put an index here

the 3 here and its index is 2 we'll put

2 here comma then you will have to put

the value that you want to replace three

and since the the error list is of

reference types you will have to use the

value of method once again and we will

3 with 30. let's run the code and see

excellent it it works out just fine

so like an array you can also sort your

right now we have added the numbers in a

if we randomize them like for example if

at the top then one after three

okay let's get rid of this indices

okay let's run the code and see what

so as you can see the numbers are all

jumbled around now to sort this error

list you will have to write the name of

in the method now you can see that there

is a small squiggly line under the sort

method name and this is because the sort

method will actually take a parameter

which is known as a comparator okay so

as you can see it says comparator in the

let me explain what this is first let's

import the comparator class so it's a

and then inside the sort method we will

order which which is a method inside the

and what we are saying is that sort this

error list in its natural order okay

let's run the code and see if it works

yeah it works just fine we have

successful­ly sorted our error list now

you can also reverse the order of this

which is similar to Natural order but

this time all the values will be sorted

there you go we have five four three two

one liftoff now three very small but

useful methods that the allergies have

is the size method the contains method

first let's see what the size method

does so if you ever want to know how

many elements are there inside an error

list you can just say the name of the

now this size method will return an

integer after counting all the elements

in the error list you can also check

whether an error list contains a certain

value or not and to do that you will

have to write contains and since

these are all reference type numbers

we'll have to use the integer Dot

value of method and we will have to put

for example one let's check if the error

see it says true which means it contains

one and if we put 10 here the output

now there is another method that checks

whether an error list contains anything

and since our analyst here actually

contains some elements the output should

and yes it is but if we clear our list

just be before checking for emptiness we

now the final thing that I would like to

now you have learned about the for Loop

already in a previous lesson and you

know that you can use it to Loop over

but when it comes to an arraylist there

is another kind of loop let me show you

how it works now keep in mind the forage

Loop looks and works a lot differentl­y

than the for Loops but I'll try my best

to explain them as lucidly as I can

list that you want to Loop over such as

then here it says action what you will

then you will make an arrow like this

and then a set of curly braces

now inside the set of curly braces you

will say something like system

and let's multiply each number with two

just as an example so you'll send number

now let's also print out the entire

arraylist at the end so numbers dot to

yeah let's run the code for now and then

I will explain what's happening inside

so as you can see we have successful­ly

multiplied each value in this error list

and we have also printed out the

original arraylist here now let me

explain the forage Loop for you so when

you are saying numbers dot for each

number you are saying that for each

number in the numbers arraylist

you want to perform the actions within

this set of curly braces or within this

so imagine this Arrow like we are

ordering the compiler like for each

number perform this action that I am

now technicall­y it's called a Lambda

expression it's it's like a method that

now of course I'm over simplifyin­g stuff

here but for now this is enough to

understand now as you can see that

although you are multiplyin­g each value

of the numbers I released we do inside

the forage Loop body the original error

now let's just for practice uh update

the original error list and replace each

value with their multiplied counterpar­ts

now to do that what we can do is

let's first print out the original

and plus yeah we are going to use the

plus sign once again in this case

and then we will take this out and we

number start doing string okay now

inside the for each Loop what we want to

dot set and inside the set of

parenthese­s we will say numbers Dot

index of which is another method that

can return the index of a given value so

using the index of method to get the

index of the current value of the number

variable and then we are updating its

element with the multiplied value okay

let's get rid of the println call here

and let's keep our fingers crossed and

yeah seems like it has worked out we

have successful­ly overwritte­n all the

values of the error list with their

multiplied counterpar­ts now this is one

of the many fun programs that you can

write to practice your skills I would

suggest that you go around the internet

find interestin­g problems that feels

challengin­g to you and solve them to

flex those Java muscles okay

now that you have learned about air

release let me show you another kind of

collection that's pretty common and

pretty useful in some scenarios these

are called hash Maps now hash maps are

actually key value Pairs and if you want

to compare it python then python

dictionari­es are kind of similar to Hash

now to work with hash Maps first you

will have to import the hashmap class

to do so you will just write import

let's get rid of all the early code and

start working on hashmap okay

Now to create a new hash map in Java you

and then just like the add list you will

have to first put the type of the key

so in my case I am making a hash map

where I'll be storing the scores for my

different subjects maybe at my school or

and the value will be the scores of the

subject so maybe English 98 maths 85 and

so on so this will be integers

and then I will name the hash map

we have successful­ly created an empty

hash map and since I have already

these wrapper classes in a previous

now to put something in this new hash

map you can use the put method

and first we will need to put the name

of the subject so it will be a string

and then a comma and then this course

I'm not that good at math so maybe 75

another subject may be a sociology

now to print out a hash map to the

console you can say system dot out Dot

exam discourse dot to string just like

okay let's run the code and see if

excellent the hash map prints out

uh so my score for English is 95

sociology 85 and math 75. uh I hope you

have already guessed that the item you

are putting into the hash map is not

sorted so even though I have put math at

first it comes out in the end so if I

what ordered this show up in the console

see as they're actually showing up in

random order but that's how hash maps

are you don't have to worry about them

now you can also print out a single

value from a hash map to do so you will

the name of the hash map then a DOT and

then you will have to pass a key in our

case the keys are all strings so I will

and yeah we are getting the score of

English now apart from the put method

there is also another method put if

absent that first checks if a value

already exists in the hash map or not

and if it doesn't then it will put it

otherwise it will just skip it now you

math and let's put a new value here

and then I would print out the entire

so as you can see the value of math is

still 75 even though I have tried to put

a new value for it but since the put if

absent method actually checks whether

math already exists or not in the hash

map it didn't override the original

value now if you want to replace one of

the values however you can use the

and it will take a key in this case we

are still working with math and we are

updating its value from 75 to 70. what a

so as you can see the value of math has

been changed to 70. now just like the

put if absent method there is another

method called get or default

a key that doesn't exist let's say for

we know that it doesn't exist in our

hash map let's see what the output is

as you can see it says null but if we

and we give it a default value of 0.

so the program will return -1 if the

now like an error list you can clear a

and this should clear out the entire

there you go and now if you want to

check the number of elements that exist

on the hash map you can do so by saying

the name of the hashmap dot size

this will return an integer after

counting all the elements present in the

hash map right now which is 0 because we

but if we get rid of that line it should

excellent to remove an item from the

hash map you can use the remove method

like this exam scores dot remove and

then you should put a name of this one

of these keys so let's get rid of

and I'll put it here semicolon then exam

as you can see sociology is not present

here now you may also want to check

whether a certain item exists on the

hatch map or not and you can do that in

either you can check for a key

or you can check for a value for example

if I want to check if the math key

exists or no I can do so by saying the

name of the hashmap exam scores dot

key and then the key I want to check

against which is math in the this case

now if I want to check if I have this

code 100 in any of the subjects or not I

can do so by saying examscores Dot

value and then the value I'm looking for

now you can also put a reference type

100 here if you want to do that

it shouldn't make any difference

yeah it just works and I have also

taught you that in case of at least when

you are trying to update one of the

values you need to pass the integer as

in reference type you can actually pass

a primitive type as well the set method

will convert it to a reference type

automatica­lly but it's up to you what

you would like to do and what you want

finally you can check if a hash map is

the name of the hash map which is

is empty and since our hashmap is not

indeed this should return false

cache Maps also have for each Loop just

like arraylist and now I will show you

an example of using them with hashmaps

to do so first you will need to write

out the name of the hashmap which is the

exams course in this case then you will

just like at least you will create a new

Lambda method here but in this case it

comma the value then the arrow and

the curly braces now the key here is the

is this Force so I'll just do it like

and then system dot out dot print Ln

Dash plus the associated score let's put

and see if it works or not okay I just

noticed that there is a small squiggly

line here that's because I didn't

enclose the two variables within a set

in case of an error list we had only one

variable so it didn't need this

parenthesi­s but since we have multiple

variables here subject and score we will

need a set of parenthese­s around them

let's run the code and see if it works

okay seems like it works now what we are

going to do we will Loop over the entire

hash map just like we did in case of the

error list and we will update the value

of each subject score just for the

purpose of practice now to do that

we already have the name of the subject

which is the key and we also have the

to update the values we will say exam

score start replace you have already

learned about this then we will subject

which is the key and then we will take

from each subject maybe for bad behavior

then we will say system dot out Dot

and exam scores dot blue string

okay I hope everything works out fine

and I cannot spot any mistakes let's hit

yeah so I have indeed taken out 10 from

each subject so English was 95 and now

it's 85 Bengali was 100 and now it's 90

sociology is 75 from 85 computer

programmin­g has become 90 from 100 and

finally math has become 65 from 75.

again I would suggest that you go into

the internet looking for problems that

you can solve to just practice all the

things you are learning in this course

this will really make you confident in

Java now that you have learned most of

the basics of java it's time that we

start discussing about object oriented

programmin­g now the concept of

object-ori­ented programmin­g in itself is

really huge and to be very honest you

cannot learn how to make good

object-ori­ented programs from a course

or a book what I can do is I can teach

you the basic concepts around

and once you have learned them you will

have to learn the rest from experience

by making larger and larger software

following good practices and so on

now at a higher level object-ori­ented

programmin­g is about modeling your

software around real life objects for

example maybe we can build a book

borrowing system where a user can come

register and login check for a book's

availabili­ty borrow it if it's available

and they can also return it on time they

can also check the list of the books

they have borrowed so far now in this

aforementi­oned system there can be two

objects one the user and two the book

we can store informatio­n such as the

user's name and birthday and in case of

a book we can store the book's title and

maybe the name of its authors and so on

so let's begin by creating a user class

in our software and as we keep working

on this simple program we will learn

about the different concepts around

object-ori­ented programmin­g so first

open up the files menu by clicking on

click on the add file button name your

Java in this file you will need to

create a new class like we have done

with the hello world file so write

user now we are declaring this class as

public because we want this class to be

available within our entire program

now inside the class we will store the

user's name which can be string so

and we will also store the user's date

local date which is a reference type for

now to use the local Red class within

our user class we will have to first

import it so import Java dot time dot

uh by the way do not get intimidate­d

about the amount of classes that Java

has built into it as you will keep

working with Java for months or maybe

for years you will eventually learn

now we have a new user class let's go

back to our hello world class and create

a new user object now creating a custom

object like a user object is not very

different from creating a string

so you will have to write user which

will be the type of our object

then you will have to name the object

maybe let's name it younger user because

we will have a older user as well later

user and a set of parenthese­s now we

have a user but this user at its current

state doesn't have any name or date of

since these variables are declared in

the class level of the user class this

will be initialize­d as null by default

so they will get default values

now variables like these at a class

and since these properties are tagged as

public we can actually access them from

outside of the user class and give some

younger user dot name equals

purse and inside the purse method we

31 which means 31st January 1995.

now the local date.burst method can pass

a date from a given string and convert

it to local date type again for using

the local date class here we will have

to first import it so import Java dot

time dot local dates then we would also

like to print something out on the

screen and for that we'll say system dot

and inside the printf method

then after the comma we will replace the

first format specifier here with the

names so we will say younger user

and then after that we would like to

replace the second format specified with

but since the birthday is not a string

you will have to first convert deep

string by calling the twisting method

and I have already said that the

twisting method usually exists in all

any local date object is actually

let's try running our program and see if

so yeah it works just fine Farhan hasin

Junior was warning back in 1995 c131

now I have already said once that using

something called Methods we can actually

Implement some Dynamic behaviors to our

for example since we have the per day of

the user we can use it to calculate

so we will create a new public method

public because we want this method to be

accessible throughout our entire program

and then we will have to write the

return type of our method which in this

case is integer because age is always an

then we will put the name of the method

and put a pair of curly braces

now from inside the method we will

calculate the age into H equals

and for that Java actually has a pretty

now this period class has some method

that you can use to calculate the

difference between two local date types

and inside this method called we will

put a starting date which is the

birthday so we will say this Dot

birthday I will explain this this later

local date dot now now this period dot

between method call will actually

calculate the difference between the

user's birthday and our current day and

then we would like to return age dot get

years because we want to return the age

in years okay we do not want anything

let's go back to our hello world class

and change this string to something like

was born back in and he is now modulus

that user was born back in the birthday

and he is now X years old so we'll put a

comma after the twisting call and say

younger user dot h and we will put a set

of parenthese­s because this is a method

and you will need to put a set of

parenthese­s to call any method in Java

let's run the program and see if it

yeah looks like everything has worked

out just fine it says foreign Junior was

0131 and he is now 27 years old

now what is this blue this keyword here

now to explain this we will actually

need two users so let's create a new

and we'll say holder user dot name

and then you will say folder user Dot

birthday equals local date Dot

okay now we'll put this system out Dot

and we'll make a copy of it at the end

of our program postponed back in uh okay

all right let's replace younger user

let's run the code and see what happens

ERS Engineers born 27 years old and this

you can see that we have two different

users in our program and both of these

users are actually created from the same

so when we are trying to calculate the

age of the user how would the computer

know which user we are referring or

which date of birth we are referring to

this is where the this keyword comes in

you see we have two instances of the

user cluster and this keyword will refer

to the current object being worked on so

when we are saying younger user dot age

then the value of this will be the

and when you are saying older user.h the

value of this would be the older user

get rid of the extra user here

change the younger user's name to just

and let's start working on the book

let's go back to the files menu create a

new file with the name book Dot Java

now let's declare a new class public

book and for a book we would like to

yeah that's pretty much it for the book

class now let's go back to the hello

and then book dot title equals to

let's put a semicolon at the end and now

so how about we implement the

functional­ity of borrowing books I will

put it in the user class so let's close

this menu as we don't need that

and we will create a new method here

and this borrow method will actually

accept a parameter because this method

has to know which book the user is

so we will say book so this method is

actually accepting variable of book type

closing and we will also have to import

the error list class so import

java.util dot arraylist okay then we can

so you're adding the book we have

received within the borrow method to our

let's go back to our hello world class

and we will pass the book to it

I think we have made a small mistake

that is we haven't said what kind of

data the borrow method is returning now

as you can see the method actually

returning nothing so we will have to say

for it which means it doesn't return

anything at all there is no return

statement whatsoever it just makes some

changes to the books error list

okay let's go back to hello world and

this looks all right so far let's update

okay let's let's write another one

and it will say modulus s has

and with some modulus s okay let's put a

comma here and we will say user dot name

uh let's also put a new line character

at the end of our printf statements

otherwise they may not look as good as

okay let's run the program and see what

happens then we will go through what

happening in this entire system once

just as I expected so as you can see it

says Farhan has engineer was born back

in 1919 and so on and then it says

Farhan has engineer has borrowed this

book's book at and then a large number

but we are expecting maybe the name of

the book or maybe the name of the author

or something like that right but that

didn't happen let me tell you why

you can see that we have been using the

method to string a lot right by using

the method twisting a lot and I have

already said that this twist string

comes with every single reference types

now our book here is a custom class and

whatever book object we are working with

now since we have created the book class

ourselves it doesn't have a built into a

string method that's why we are getting

now to solve this problem we will have

to implement a twisting method we can do

and then we will return a string

representa­tion of this book like return

string dot format here and we'll say

modulus is then a full stop and after

and this dot author so whenever we are

trying to access one of the properties

within a class from a method within the

same class we can use that this keyword

okay let's try to run the program once

again and see if it solves our issue or

let's make our console bigger

I think that full stop there looks

pretty bad because it's going to show up

and also I think this is a good time to

switch back to the Stacked layout once

again since our codes are getting bigger

horizontal­ly and this gives us a better

okay so what have we done so far we have

created two custom classes representi­ng

our users and the books we have created

a new user object we have given him the

ability to borrow books from us we have

also calculated their age using method

we have implemente­d title and author for

our books and we have also implemente­d

accustomed to string method so this is

really a lot to be honest but we will do

more now so far we have been declaring

all our methods and our properties as

public but to be very honest this is not

something you should be doing a lot

let's learn about something called a

as you can see when you are trying to

create a new user you are saying user

then name of the user object equals new

and then you are writing the name of the

class once again and then a set of

parenthese­s as if you are trying to call

every single class that we have in Java

has a special method called Constructo­r

this method is responsibl­e for

initializi­ng all the properties with

their default values so what we can do

is we can customize these Constructo­r

let's start by writing a Constructo­r for

user and will not write anything like

public or maybe some sort of return type

nothing at all we will just start by

writing what the name of the class is

then we will put a set of parenthese­s

and set of curly braces so this is our

Constructo­r method now let's think about

what we want from the user when they are

creating a new user object right

we want their name so we will receive or

ask for their name and we will also ask

can be taken as a local date but we will

now inside this Constructo­r method we

birthday equals local date dot purse

so what we are doing essentiall­y is we

are asking the user for a name and we

are storing that name in the name

variable or name property within the

user class then we are also asking for a

birthday and we are storing that

birthday in the birthday property but

since the birthday property is of type

local date we will have to purse the

birthday from a string format to local

date format now let's go back to our

hello world class and make the necessary

changes here we will say user equals

user and we will put the name

inside this Constructo­r call and we'll

put a comma here and we'll also put the

within the Constructo­r call because now

the user class is capable of accepting

these two values let's run the code and

see if everything works just as before

seems like I have made a small typo here

the D should have been capital

since we can initialize the user with a

name and a date of birth right at the

we can actually make the name and

which means we can no longer do things

user dot birthday or user dot name

but we still need to know the user's

for that we have something called

so we will create a new method

somewhere in this user class public

and the return type B string

and we will say return this dot name

and we will also say public string get

and you will say return this dot

now let's go back to the hello world

class and make use of these two Getters

we will come down to printf and we will

birthday and we'll get rid of the two

string calls since the birthday will

come back as a string by default

now let's run the code and see how it

okay we also have to replace this name

here and as you can see since we have

made the name properties private the

hello world class actually fails to

access the user's name which is a good

I will explain why let's just make it

so yeah it's it's back to normal now

the name and birthday properties have

become private no one can change their

values from outside the user class

which means these are now much more

secret than they were before another

thing that is now we can pass the name

and the birthday as a strings the hello

world class has no business in knowing

what is the actual type of the birthday

all the Hello World Class needs to know

that if it passes a user name and a

birthday in string format a new user

so what we are doing is we are hiding

the complexiti­es of the user class

behind this beautiful looking Gator

methods Constructo­r methods you can

already see how cleaner the user object

creation looks compared to the book

let's make the same changes to the book

class as well so we will go back to it

then we will Implement to getter methods

return this title the return type will

and then we will say public

get author and we say return this Dot

let's also implement the Constructo­r so

we will take the title as a string and

then we will take the author name as a

then we will set this dot title equals

let's update the creation process so we

will pass the title of the book and the

with the new keyword and get rid of that

excellent the program already looks much

cleaner now another thing that I would

like to change is I would like to make

the books list private and Implement a

getter for that as well so let's go back

to the user class and let's say

and this time we will be returning

and we'll say return peace dot books dot

now the hello world class doesn't know

about the complexiti­es of the books list

did I meet it private yet no I didn't so

okay let's see if the program works just

excellent the program works just as

now I hope you can already see the

beauty of object rendered programmin­g

and how cleaner the program actually

we still have to learn a few more

Concepts around object entry programmin­g

such as inheritanc­e now assume that our

book borrowing system has multiple types

of booths there can be the regular books

I mean the hardcover ones or the printed

ones then there can be ebooks and there

can be audio books now although they

have some similariti­es they also have

the ebooks and the regular books have

page counts where the audio books have

also the ebooks have formats such as PDF

or ePub or so on so trying to implement

different kinds of books using the same

now you may think that you will make

copies of the book class and add or

remove the necessary properties methods

to them but that's not a very good idea

this is why inheritanc­e comes in

so we can make a default book class with

the most common properties and methods

child book classes that will inherit all

the properties and methods from the

parent book class and we can also add

some new properties and methods to them

let's see an example first we will add

the page count property to the book so

and for that we will have to pass

the page count to the Constructo­r here

so we'll set this Dot Page count equals

we'll go back to our hello world class

I don't remember the actual page count

of the book but let's put 270.

nice everything should be normal let's

ah that was a silly mistake I didn't

let's run the program and make sure

now we will create a new audio book

book now since we are declaring this

audiobook class as an extension of the

parent book class it already has

all these properties and methods we have

so what we need to add is a runtime so

how long these audio books run so the

a new Constructo­r here so we'll say

just like before and we will accept the

and then inside the pair of curly braces

runtime now here is a problem I have

already said that since this audiobook

class is an extension of the book class

it also inherits all these private

properties which means we will still

but the audiobook Constructo­r

doesn't accept any of these values

okay let's see what we can do to solve

this first we'll copy all these

parameters from the book Constructo­r

and add them to the audiobook

one of the problems have been solved we

are now accepting all the necessary

informatio­n for the parent book class

now the super keyword here actually

refers to the parent class of our

current class so when you are calling

the method super we are actually calling

the Constructo­r of the parent book class

so we have successful­ly filled up all

the necessary properties of the parent

class as well let's try out by creating

let's go back to the hello world class

actually we do not have to pass the page

count here we can modify our Constructo­r

a little bit we do not need to accept

instead we can pass 0 as the page count

yeah that would be better and we can

so for example maybe the Dracula book

would run for 30 000 minutes so I put 30

audiobook see I have made a mistake

start naming our books so carmilla

okay so we have successful­ly created a

new audio book here just for the sake of

our codes Clarity let's get rid of all

the code that we do not need so we will

the user dot borrow call we have seen

examples of that we will also get rid of

the system.out­.printf calls we will get

rid of the user as well because for now

we will be focusing strictly on books

system.out­.printf method here

because remember that the audiobook

class already inherits the two string

okay let's print out something on the

screen so it's a system dot out dot

and Dracula dot Google string

let's run the code and see if it works

yeah it works just fine okay now that we

have a audiobook class let's create a

and then within the set of curly braces

uh actually we can copy a bunch of code

copy everything to the ebook class

everything and we will also accept the

page count this time because ebooks have

so input page account and then we will

also accept the format so we'll say

this dot format equals one CF

nice uh yeah everything looks fine okay

we have to change this to ebook

let's go back to hello world and try to

create a new ebook Okay so ebook

so Jeeves I will create a Chiefs book

old house I hope I'm spelling his name

then the page count would be 280 I guess

and finally the format will be PDF

let's put a semicolon there and let's

see if the book has been created

properly or not so Jeep stop to stream

okay so carry on Jeeps by PG Port house

so we have successful­ly created

different kinds of books based on a

now this is what I had in store for this

course in terms of object oriented

programmin­g I have taught you what are

classes what are objects water

properties and methods Constructo­r

methods and you have also learned about

now there are a lot of things that you

will have to still learn like method

overloadin­g and overriding Abstract

method and whatnot but I would not like

to overwhelm you with all these Concepts

what I would suggest that try to

understand everything that I have taught

you in this course uh as thoroughly as

you can and then keep practicing make

programs make bigger programs and try to

understand whatever concept seems

complex to you and as you keep working

with Java as you keep making more and

more fun projects you will start to

understand a lot of the complex Concepts

around object oriented programmin­g and

so I hope you have learned something

good from this course and maybe someday

I will see you in another course as well

so till then stay safe and take care