'this' reference in Java

‘this’ is a reference variable that refers to the current object.

Following are the ways to use ‘this’ keyword in java :

1. Using ‘this’ keyword to refer current class instance variables

//Java code for using 'this' keyword to 
//refer current class instance variables 
class Test 
{ 
    int a; 
    int b; 
      
    // Parameterized constructor 
    Test(int a, int b) 
    { 
        this.a = a; 
        this.b = b; 
    } 
  
    void display() 
    { 
        //Displaying value of variables a and b 
        System.out.println("a = " + a + "  b = " + b); 
    } 
  
    public static void main(String[] args) 
    { 
        Test object = new Test(10, 20); 
        object.display(); 
    } 
} 

Output:

a = 10  b = 20

2. Using this() to invoke current class constructor

// Java code for using this() to  
// invoke current class constructor 
class Test 
{ 
    int a; 
    int b; 
  
    //Default constructor 
    Test() 
    {   
        this(10, 20); 
        System.out.println("Inside  default constructor \n"); 
    } 
      
    //Parameterized constructor 
    Test(int a, int b) 
    { 
        this.a = a; 
        this.b = b; 
        System.out.println("Inside parameterized constructor"); 
    } 
  
    public static void main(String[] args) 
    { 
        Test object = new Test(); 
    } 
} 

Output:

Inside parameterized constructor
Inside  default constructor

3. Using ‘this’ keyword to return the current class instance

//Java code for using 'this' keyword  
//to return the current class instance 
class Test 
{ 
    int a; 
    int b; 
  
    //Default constructor 
    Test() 
    { 
        a = 10; 
        b = 20; 
    } 
      
    //Method that returns current class instance 
    Test get() 
    { 
        return this; 
    } 
      
    //Displaying value of variables a and b 
    void display() 
    { 
        System.out.println("a = " + a + "  b = " + b); 
    } 
  
    public static void main(String[] args) 
    { 
        Test object = new Test(); 
        object.get().display(); 
    } 
} 

Output:

a = 10  b = 20

4. Using ‘this’ keyword as method parameter

// Java code for using 'this'  
// keyword as method parameter 
class Test 
{ 
    int a; 
    int b; 
      
    // Default constructor 
    Test() 
    { 
        a = 10; 
        b = 20; 
    } 
      
    // Method that receives 'this' keyword as parameter 
    void display(Test obj) 
    { 
        System.out.println("a = " +obj.a + "  b = " + obj.b); 
    } 
   
    // Method that returns current class instance 
    void get() 
    { 
        display(this); 
    } 
  
    public static void main(String[] args) 
    { 
        Test object = new Test(); 
        object.get(); 
    } 
} 

Output:

a = 10  b = 20

5. Using ‘this’ keyword to invoke current class method

// Java code for using this to invoke current  
// class method 
class Test { 
  
    void display() 
    { 
        // calling function show() 
        this.show(); 
     
       System.out.println("Inside display function"); 
    } 
      
    void show() { 
        System.out.println("Inside show funcion"); 
    } 
      
  
    public static void main(String args[]) { 
        Test t1 = new Test(); 
        t1.display(); 
    } 
} 

Output :

Inside show funcion
Inside display function

6. Using ‘this’ keyword as an argument in the constructor call

// Java code for using this as an argument in constructor 
// call 
// Class with object of Class B as its data member 
class A 
{ 
    B obj; 
      
    // Parameterized constructor with object of B  
    // as a parameter 
    A(B obj) 
    { 
        this.obj = obj; 
         
     // calling display method of class B 
        obj.display(); 
    } 
      
} 
  
class B 
{ 
    int x = 5; 
      
    // Default Contructor that create a object of A  
    // with passing this as an argument in the  
   // constructor 
    B() 
    { 
        A obj = new A(this); 
    } 
      
    // method to show value of x  
    void display() 
    { 
        System.out.println("Value of x in Class B : " + x); 
    } 
      
    public static void main(String[] args) { 
        B obj = new B(); 
    } 
} 

Output :

Value of x in Class B : 5

This article is contributed by Mehak Narang and Amit Kumar.

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‘this’ reference in Java

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