This Keyword in Java

Last Updated: 28 May, 2022

‘this’ is a reference variable that refers to the current object/instance whose method or constructor is being invoked. You can refer to any member of the current object from within an instance method or a constructor by using this.

User Cases of 'this' Keyword

Example 1 : ‘this’ keyword referring current class instance variables

class Digits { // Instance Variables public int x = 100; public int y = 0; // Constructor with two parameters public Digits(int x, int y) { // Assigning local variables values in instance variables this.x = x; this.y = y; } void showNumbers() { System.out.println("x: " + x); System.out.println("y: " + y); } } public class ThisWithVariables { public static void main(String[] args) { Digits digits = new Digits(20, 40); digits.showNumbers(); } }

Output

x: 20
y: 40

Example 2 : Using this() to invoke current class constructor

class Demo { int a; int b; int c; // Default constructor Demo() { // Calling 2 parameterized constructor this(10, 20); System.out.println("\n1. Default Constructor called."); } // Parameterized Constructor with 2 parameters Demo(int a, int b) { // Calling 3 parameterized constructor this(a, b, 30); System.out.println("\n2. Parameterized constructor with 2 parameters called."); } // Parameterized Constructor with 3 parameters Demo(int a, int b, int c) { // Assigning local variables values in instance variables this.a = a; this.b = b; this.c = c; System.out.println("3. Parameterized constructor with 3 parameters called."); System.out.println("Values => a :" + a + " b: " + b + " c: " + c); } } public class ThisWithConstructorCalling { public static void main(String[] args) { // Creating an object with default constructor Demo object = new Demo(); } }

Output

3. Parameterized constructor with 3 parameters called.
Values => a :10 b: 20 c: 30

2. Parameterized constructor with 2 parameters called.

1. Default Constructor called.

Example 3 : Using ‘this’ keyword to call current class method

class Test { void show() { System.out.println("A - show() method"); } void display() { // Calling current class method using this keyword this.show(); System.out.println("A - display() method"); } } public class ThisWithMethods { public static void main(String[] args) { Test obj = new Test(); obj.display(); } }

Output

A - show() method
A - display() method

Example 4 : ‘this’ keyword as an argument in constructor calling

class First { Second secondObj; // Second class object as a constructor parameter First(Second obj) { this.secondObj = obj; // calling print method of class Second secondObj.print(); } } class Second { Second() { First obj = new First(this); } void print() { System.out.println("Second Class => print() method called"); } } public class ThisAsConstructorArgument { public static void main(String[] args) { // Creating an object of Second class Second secObj = new Second(); } }

Output

Second Class => print() method called

Example 5 : Passing ‘this’ keyword as a method parameter

class Demo { int x; int y; // Default constructor Demo() { x = 10; y = 20; } void print(Demo demoObj) { System.out.println("x = " + demoObj.x + " y = " + demoObj.y); } void callerMethod() { // Passing 'this' keyword as parameter print(this); } } public class ThisAsMethodParameter { public static void main(String[] args) { Demo obj = new Demo(); obj.callerMethod(); } }

Output

x = 10 y = 20

Example 6 : Returning ‘this’ keyword as a current class instance

class Demo { // Instance Variables int x; int y; // Default constructor Demo() { x = 10; y = 20; } // Returning current class instance Demo getInstance() { return this; } void print() { System.out.println("x => " + x + " y => " + y); } } public class ThisReturnCurrentClassInstance { public static void main(String[] args) { Demo demoObj = new Demo(); demoObj.getInstance().print(); } }

Output

x => 10 y => 20