Use the keyword this to call a constructor

Byron KiourtzoglouNovember 11th, 2012Last Updated: July 21st, 2013

0 39 1 minute read

In this example we shall show you how to use the keyword this to call a constructor in a class. Within an instance method or a constructor, this keyword is a reference to the current object, that is the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this keyword. To use the keyword this to call a constructor we have performed the following steps:

We have created a class UseOfThis, that has two final fields, MAX_X and MAX_Y. It also has two int fields, a and b.
It has a constructor to initialize its two int fields, using this keyword to get the object’s fields with two given int fields.
It has another constructor without fields, that calls the previous constructor, using this keyword, with arguments the two final fields divided by two.
It also has a toString() method that returns the int values.
We create a new instance of UseOfThis using two int fields as arguments. Then we create another UseOfThis instance without fields. This constructor calls the first constructor as described above,

as described in the code snippet below.

package com.javacodegeeks.snippets.core;

public class UseOfThis {

    final static int MAX_X = 640, MAX_Y = 480; 
    int a, b;

  
    UseOfThis(int a, int b) {

  this.a = a;

  this.b = b;
    }

    UseOfThis() {

  this(MAX_X / 2, MAX_Y / 2);   // Use the constructor above
    }

    public String toString() {

  return "[" + a + "," + b + "]";
    }

  
    public static void main(String[] av) {

  System.out.println(new UseOfThis(300, 100));

  System.out.println(new UseOfThis());
    }
}

Output: