What is this keyword in java best program

this keyword in java:- this keyword is a special reference variable that holds the object address and it gets created automatically when we create an object.

this keyword in java with Program

Example 1

public class A{  
	
	public static void main(String[] args) {
     A a1 = new A();
       a1.test();
	}
	public void test() {
		System.out.println(this);
	}
}

Output:  A@2c7b84de

Example 2 – this keyword in Java program

public class A{ 
	int x=100;
	public static void main(String[] args) {
     A a1 = new A();
     a1.test();
     System.out.println(a1.x);
	}
	public void test() {
		System.out.println(this.x);
	}
}

Output: 
100
100

Note1: – Using this keyword we can access non-static members.

public class A{ 
	int x=100;
	public static void main(String[] args) {
     A a1 = new A();
     a1.test1();
     System.out.println(a1.x);
	}
	public void test1() {
		this.test2();
	}
	public void test2() {
		System.out.println("Raju");
	}
}

Output: 
Raju
100

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Note2: – this keyword points to the current object running in the program.

public class A{ 
	public static void main(String[] args) {
    A a1 = new A();
    a1.test();
    A a2 = new A();
    a2.test();
    a1.test();
	}
	public void test() {
		System.out.println(this);
	}
}

Output: 
A@2c7b84de
A@3fee733d
A@2c7b84de

Limitation of this keyword in java Program

1. We can not use this keyword inside the static method to enhance the below program throws an error.

public class A{ 
	public static void main(String[] args) {
    System.out.println(this);  //Error
	}
}

2. using this keyword we can access non-static variables but we should not be done.

public class A{ 
	int x=10;
	public static void main(String[] args) {
    A a1 =new A();
    a1.test();
	}
	public void test() {
		System.out.println(this.x);
	}
}

Output: 10

3. Using this keyword we can access the static method ensured in the below program.

public class A{ 
	public static void main(String[] args) {
    A a1 =new A();
    a1.test();
	}
	public void test() {
		this.raj();
	}
	public static void raj() {
		System.out.println("Learn Java");
	}
}

Output : Learn Java

Uses of this() keyword in java with Program

1. this() – it is used to call the constructor.

public class A{ 
	A(){
		System.out.println("Learn Java");
	}
	A(int x){
		this();
		
	}
	public static void main(String[] args) {
  A a1 = new A();
	}
}

Output : Learn Java

Example 2

public class A{ 
	A(){
		this(10);
	}
	A(int x){
		System.out.println(x);
		
	}
	public static void main(String[] args) {
  A a1 = new A();
	}
}

Output: 10

2. While calling the constructor using this() keyword ensure that this calling is being done from another constructor only. hence the below program throws an Error.

public class A{ 
	A(){
	System.out.println("Learn Java");
	}
	public static void main(String[] args) {
  A a1 = new A();
  a1.test();
	}
	public void test() {
		this();  //Error
	}
}

3. While calling a constructor using this() keyword it has to be always the first statement inside another constructor.

public class A{ 
	A(){
		
	System.out.println("Learn Java");
	}
	A(int x){
		System.out.println(1000);
		this();   // Error
	}
	public static void main(String[] args) {
  A a1 = new A();
	
	}
}