Learn with Youtube video –  

💡this –

💡Definition-

It’s a keyword which refers to current class.
this keyword is used to-

Use of this keyword	Description	Example
this as variable	this is a reserved word in Java that refers to the current instance of the class. It can be used to access instance variables and methods of the current object.	this.x = 10;
this as current class constructor	this can be used to call another constructor of the same class from a constructor. This is known as constructor chaining.	public MyClass() { this(0, 0); }
this as current class method	this can be used to refer to the current object from within a non-static method of a class. It can be used to access instance variables and methods of the current object.	public void setValues(int x, int y) { this.x = x; this.y = y; }
this as argument in method call	this can be passed as an argument to a method to indicate that the method should operate on the current object.	obj.printValues(this);
this as argument in constructor call	this can be passed as an argument to a constructor to indicate that the constructor should create an instance of the current class.	MyClass obj = new MyClass(this);
this as class instance	this can be used to create an instance of a class. For example, MyClass obj = new this(); creates an instance of the MyClass class.	MyClass obj = new this();

💡(1) Refer class variable –

 package dis;

public class TisVar{

String name="Kuldeep";

void show(){
System.out.println(this.name); //here
}

public static void main(String[] args){
TisVar tvObj = new TisVar();
tvObj.show();
}

}

Run this Program 

💡(2) Refer current class constructor-

 package dis; public class TisConst{

public TisConst(){

this(5);

System.out.println("Kuldeep");

}

public TisConst(int age){

System.out.println("kaushik");

}

public static void main(String[] args){
TisConst k=new TisConst();
}

}

Run this Program 

💡(3) Invoke current class method-

 package dis;

public class TisMtd{

void show(String name){

System.out.println(name);

}

void disp(){

this.show("kuldeep");

}

public static void main(String[] args){
TisMtd tisObj = new TisMtd();
tisObj.disp();
}

}

Run this Program 

💡(4)this : passed as an argument in method call

 package dis;

public class TisMtdArg{

String name = "kuldeep";

void show(String name){

System.out.println(name);

}

void disp(){

this.show(this.name); //here

}

public static void main(String[] args){
TisMtdArg tisObj = new TisMtdArg();
tisObj.disp();
}

}

Run this Program 

💡(5)this : passed as an argument in constructor call

 package dis;

public class TisConstArg{

int age = 12;

void show1(){

new TisConstArg(this.age);

}

public TisConstArg(int age){

System.out.println("Kuldeep - Age = "+age);

}

public static void main(String[] args){
TisConstArg tisConstArgObj = new TisConstArg(30);
}

}

Run this Program 

💡(6)this: can be used to return the class instance

 package dis;

public class TisClsIns{

TisClsIns currentIns(){

return this; //here

}

public static void main(String[] args){
TisClsIns tisClsInsObj = new TisClsIns();
TisClsIns tisClsInsObj2 = tisClsInsObj.currentIns();
System.out.println(tisClsInsObj2);
}

}

 

Run this Program 

💡2]:- SUPER KEYWORD:-

💡Definition-

It’s a keyword which refers to parent class.

super keyword is used to –

Use of super keyword	Description
super.variable	A reference to a parent class variable. Can be used to access the value of the variable or to assign a new value to it.
super.method()	A reference to a parent class method. Can be used to call the method from the child class.
super()	A reference to a parent class constructor. Must be the first statement in a subclass constructor and is used to initialize the parent class before the child class.

💡1:- Refer parent class instance variable.

 package spr; class SperVar{
int age =10;
}
public class SuprVar extends SperVar {
int age=20;
void show(){
System.out.println(super.age);
}
public static void main(String[] args){
SuprVar suprVarObj = new SuprVar();
suprVarObj.show();
}
}

Run this Program 

💡2:- Refer parent class constructor.

 package spr; class SperConst{
SperConst(){
System.out.println("parent");
}
}
public class SuprConst extends SperConst {
SuprConst(){
super();
System.out.println("child");
}
public static void main(String[] args){
SuprConst s1=new SuprConst();
}
}

Run this Program 

💡3:-Refer parent class method

package spr;
<div class="line number2 index1 alt1">

class SperMtd{
void show(){
System.out.println("parent");
}
}

public class SuprMtd extends SperMtd{
void show(){
super.show();
System.out.println("child");
}
public static void main(String[] args){
SuprMtd s1=new SuprMtd();
s1.show();
}
}
</div>
<div class="line number15 index14 alt2"><code class="java plain"></code>

Interview Questions —

• What ‘this’ keywords refers to ?
• What ‘that’ keywords refers to ?