What is ‘this’ reference in Java?

The this is a keyword in Java which is used as a reference to the object of the current class, with in an instance method or a constructor. Using this you can refer the members of a class such as constructors, variables and methods.

Using “this” you can −

• Differentiate the instance variables from local variables if they have same names, within a constructor or a method.

class Student {
   int age;
   Student(int age) {
      this.age = age;
   }
}

• Call one type of constructor (parametrized constructor or default) from other in a class. It is known as explicit constructor invocation.

class Student {
   int age
   Student() {
      this(20);
   }
   Student(int age) {
      this.age = age;
   }
}

Example

 Live Demo

public class This_Example {
   // Instance variable num
   int num = 10;
   This_Example() {
      System.out.println("This is an example program on keyword this");
   }
   This_Example(int num) {
      // Invoking the default constructor
      this();
      // Assigning the local variable num to the instance variable num
      this.num = num;
   }
   public void greet() {
      System.out.println("Hi Welcome to Tutorialspoint");
   }
   public void print() {
      // Local variable num
      int num = 20;
      // Printing the local variable
      System.out.println("value of local variable num is : "+num);
      // Printing the instance variable
      System.out.println("value of instance variable num is : "+this.num);
      // Invoking the greet method of a class
      this.greet();
   }
   public static void main(String[] args) {
      // Instantiating the class
      This_Example obj1 = new This_Example();
      // Invoking the print method
      obj1.print();
      // Passing a new value to the num variable through parametrized constructor
      This_Example obj2 = new This_Example(30);
      // Invoking the print method again
      obj2.print();
   }
}

Output

This is an example program on keyword this
value of local variable num is : 20
value of instance variable num is : 10
Hi Welcome to Tutorialspoint
This is an example program on keyword this
value of local variable num is : 20
value of instance variable num is : 30
Hi Welcome to Tutorialspoint

Narasimha Murthi

Published on 05-Jul-2019 09:02:34

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