DEV Community: Sahithi Puppala

core java -Basics

Sahithi Puppala — Tue, 02 Jul 2024 09:16:53 +0000

Day-4:

Today We learn about Some important topics are you excited

Java Class:

java Class is Divided into 2 types:
1)Predefined Class
2)User defined class

1)Predefined Class:

Every java Predefined Class always start with CAPITAL LETTERS

[EX: System, String...etc]

2)User defined class:

Java user defined Classes start with Both SMALL and CAPITAL LETTERS
It is highly advisable to start a java class name with CAPITAL LETTER.

Java Method:

java Method is Divided into 2 types:
1)Predefined Method
2)User defined Method

1)Predefined Method:

Every Java Predefined Method always starts with a Small letter.

2)User defined Method:

Every Java user defined Method Can starts with Both Small letters and Capital letters.

Note: Predefined Method, User defined Method again divided into 2 types Parameterized Method and Non-Parameterized Method.

Main Method:

Main() is a Parameterized Method ,in 1 Parameter ,Type is String Array.

Inside a Parentheses we could write Parameters or Arguments.

Example:
public class ClassA
{
void Meth1(int i) //parameterized method
{
System.out.println("Meth1() Called");
System.out.println("i value:" +i);
}
void Meth2(int i,String S, char C) //parameterized method
{
System.out.println("Meth2() Called");
System.out.println(i-99);
System.out.println(S);
System.out.println(C);
}
public static void main(String[] args)
{
ClassA aobj=new ClassA();
aobj.Meth1(99);
System.out.println("-------------------");
aobj.Meth2(100,"Hello",'X');
}
}

OUTPUT:

Meth1() Called
i value:100

Meth2() Called
1
Hello
X

Important Question for Interview Purpose
Q)What happens internally whenever we are compiling and running a java program?
A: When ever we are Compiling our java Program with the help of the Command Javac Filename.java , java compiler is going to compile our java program. After Successful Compilation it is going to generate a .Class file. The generated .class file Consists of byte code instructions which cant be understandable by the humans. Those byte code instructions can be understandable only by the machines. in our scenerio that machine is JVM. In order to run our java program we need to provide the generated .Class file as an input of the jvm with the help of command java generated .class file name jvm is going to check whether all the byte code instructions present in that .Class file are correct or wrong ,if correct we will be getting the output. If Wrong We will getting an exception.

Waiting for Day-5------------------------------------------------------

core java -Basics

Sahithi Puppala — Sat, 29 Jun 2024 09:37:05 +0000

DAY-3

Today we will discuss about object!

OBJECT:

==>Object are created from a Class.
==>An Object is a Real world entity.
==>In order to Create a class object first we need to write "new" keyword and initialize that object with the help of a constructor, constructor name will be same as class name.
==>We can create any number of object from a Class.

Example:
ClassA aobj = new ClassA(); //ClassA object
ClassB bobj = new ClassB(); //ClassB object
ClassC cobj = new ClassC(); //ClassC object

I write a simple program to understand the how to create Class Object.

public class First { public void msg() { System.out.println("HELLO WORLD"); } private void display() { System.out.println("java is awesome"); } public static void main(String[] args) { System.out.println("Start"); First obj=new First(); //Creating an object obj.msg(); //Calling a method obj.display(); //calling a method System.out.println("End"); } }

OUTPUT:
Start
HELLO WORLD
java is awesome
End

Every Program to Run in java we can do 2 specific tasks:
1)Compilation
2)Running

Compilation:

[java Compiler==>javac Filename.java]

Here Compilation do Java Compiler, java Compiler Command is Javac Filename.java.
Compilation means checking the code whether we have written according to the java language Syntax or not.
After Successful Compilation java Compiler is going to generate a .Class file .
The generated .Class File name will be same as Class name.
The generated .Class file Consists of bytecode instructions which are understand only by the machines , humans Can not understand them.

Running:

[JVM(Java Virtual Machine)==>java generated .Class File name]

In order to run our java program we need to send our generated .Class File as input to the JVM.
JVM is going to check whether all the byte code instructions present in the .Class file are Correct Or Wrong if Correct will be getting Output if Wrong we will be getting an Exception.

Waiting for Day-4-----------------------------------------------------

core java-Basics

Sahithi Puppala — Fri, 28 Jun 2024 07:18:29 +0000

Day-2

Let's Continue..........................................

in java we are having '3' basic Programming elements we know

1) Class [Class is use above 90% in java]
2) Interface [Interface is use in 8 to 10% ]==>when we use -"if we want to achieve abstraction. "
3) Enum [we use less than 2%]==>When we use-"if our project is having universal constants"

LET'S GOTO THE IMPORTANT TOPIC IN JAVA ---JAVA METHOD

Q)WHAT IS A JAVA METHOD?
A:It is a place where we will be writing the 'Business Logic'

i think you all are one doubt!!!
==>what is BUSINESS LOGIC-"Business logic is any kind of code."

Lets go learn Syntax of a java Method ?

()
{
----------;
----------; //Method body/Functionality/implementation
----------;
}

Note :()-Parenthesis

We know what is Access Modifiers let's learn 'Return Type'

Return Type:

 We are having '4' options for returning a value from a method

1)void
2)We can use all the '8' Primitive datatypes.[int ,byte ,short ,long ,float ,double ,char ,boolean]
3)Classes
4)Interfaces

in java mostly used in void return type why because

void -No Need to Return anything

Example:
Public void meth()
{
-------;
}

==>we can write any number of methods inside a class.
==>A java Method will be executed "ONLY" whenever we are calling it.
==> We need to call a method with the help of its "Respective" Class Object.

Note:
1) Every java Program execution start from main() and ends with main()
2)main() is like a entry point our program.
3)Without writing main() in our Program we will not be able to run our code.

We will discuss what is object!!!
waiting for Day-3 ----------------------------------------------------

core java-Basics

Sahithi Puppala — Fri, 28 Jun 2024 06:30:51 +0000

Day 1

i am also beginner , lets learn together🤓

BASIC JAVA PROGRAMMING:

         "in java if you want write any code in java we need to take the hype of CLASS or INTERFACE or ENUM." 


                  1.Class
                  2.Interface
                  3.Enum

First we learn each one syntax's !!!

Wait............................

Q)WHAT IS SYNTAX?
A: Syntax means Some set of rules which we need to follow whenever we are writing the code if we are not following the syntax we will be getting an error.

CLASS:

---->Syntax of Class:
Class
{
------;
------;
}

Example:
Public Class ClassA
{
-----;
-----;
}

INTERFACE:

---->Syntax of Interface:
< Access Modifier > Interface
{
-------;
-------;
}

Example:
Public Interface ClassA
{
-----;
-----;
}

ENUM:

---->Syntax of Enum:
Enum
{
-------;
-------;
}

Example:
Public enum ClassA
{
-----;
-----;
}

i think you all are one doubt in your mind!!!

What is Access Modifiers?

Access Modifiers:

             Access Modifiers Provide Access Restrictions Which Will enhance the data Security.in java We are having '4' access Modifiers.

               1.Public
               2.Private
               3.Protected
               4.Package-Private(default)

Note: We can use only '2' access Modifiers for a java Class, they are Public & Package-Private(Default).

waiting for Day-2 ....................................................