why does this keyword in constructor gives different result?

Question

I don't Understand why Default constructor is executed after parameterized constructor in this program ?

class A{
  int a , b;

  A(){
    this(10,20);
    System.out.println("Inside Default Constructor values:"+a+" "+b);
  }

  A(int a , int b){
    this.a=a;
    this.b=b;
    System.out.println("Inside Parameterized Constructor values:"+a+" "+b);
  }
}

public class thisExample {
  public static void main(String[] args) {
    A obj = new A();
  }
}

This gives output as :

Inside Parameterized Constructor values:10 20
Inside Default Constructor values:10 20

it is not. you just log after parameterized executed. actually parameterized is executed within default — pirho, Nov 20 '17 at 19:31
This looks like a *great* opportunity to use a debugger to step through the code, line by line, and observe how it behaves. You'll find that each statement tends to execute in the order in which it is invoked. — David, Nov 20 '17 at 19:34
Related: [How do I call one constructor from another in Java?](https://stackoverflow.com/q/285177) — Pshemo, Nov 20 '17 at 19:51
Before posting this question I expect default constructor excutes 1st and then parameterized constructor. Now I understand how it works. Thanks for your time. — Balaji, Nov 21 '17 at 12:05

score 2 · Answer 1 · answered Nov 20 '17 at 19:34

Its clear from your code why its happening

A obj = new A();

calls your default constructor

A(){
    this(10,20);
    System.out.println("Inside Default Constructor values:"+a+" "+b);
}

which further calls yours parametrized constructor first this(10,20); so your code prints Inside Parameterized Constructor values:10 20 first and than it prints Inside Default Constructor values:10 20

score 1 · Answer 2 · answered Nov 20 '17 at 19:33

1

The first statement in the default constructor executes the parameterized constructor. You can include the sysout before executing the this(10, 20) and check the behavior.

answered Nov 20 '17 at 19:33

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why does this keyword in constructor gives different result?

2 Answers2