Constructor call must be the first statement in a constructor [duplicate]

Question

I do not understand why the below code displays the error Constructor call must be the first statement in a constructor if I shift this(1); to the last line in the constructor.

package learn.basic.corejava;

public class A {
    int x,y;

    A()
    {     
        // this(1);// ->> works fine if written here
        System.out.println("1");
        this(1);  //Error: Constructor call must be the first statement in a constructor
    }

    A(int a)
    {
        System.out.println("2");
    }

    public static void main(String[] args) { 
        A obj1=new A(2);  
    }   
}

I've checked many answers on this topic on StackOverflow but I still could not understand the reason for this. Please help me to make clear about this error with some easy example and explanation.

Answer 1

As you know, this works:

A() {
      this(1);
      System.out.println("1");
}

Why? because it's a rule of the language, present in the Java Language Specification: a call to another constructor in the same class (the this(...) part) or to a constructor in the super class (using super(...)) must go in the first line. It's a way to ensure that the parent's state is initialized before initializing the current object.

For more information, take a look at this post, it explains in detail the situation.

Answer 2

The error tells you the problem

A()
{     
      System.out.println("1");
      this(1);  //Error: Constructor call must be the first statement in a constructor
}

i.e. you must call the constructor first

A()
{
      this(1);
      System.out.println("1");
}

this also applies to calls to super

class B extends A
{
    B()
    {
        super();
        System.out.println("1");
    }
}

the reason being is answered here