Calling an overloaded constructor of superclass in Java

Question

In java, can a contructor in a class call an overloaded constructor of its superclass (say if we wanted to make that call explicitly and deliberately).

I know that a constructor in a class makes implicit call to no-arg default constructor of superclass (with super(); ). But suppose I make a call to an overloaded superclass constructor (say super(String s); ), then my question is, Is this possible? And if this is possible, then is a call to super() still made ahead of super(String s) or not and what are its implications?

Answer 1

Yes, you can call an overloaded constructor of the superclass. And that should be the first statement inside the constructor.

And no, you can only invoke the superclass's constructor once, so a call to super(args) would substitute the implicit call to super() . For the example:

A.java

public class A {
    private String fieldA;

    public A(String a) {
        fieldA = a;
    }
}

B.java

public class B extends A {
    private int fieldB;

    public B(String a, int b) {
        // Call the overloaded constructor of the class A
        super(a); // replaces the implicit call to super()
        fieldB = b;
    }
}

but if you do this, you will get an error because the call to super() is not the first statement of the constructor:

public B(String a, int b) {
    fieldB = b;
    super(a); // Call to super() must be first statement in constructor body
}

Answer 2

Yes, we can override super-class's constructor call, while override super-class's default constructor call it will not skip/avoid to call default constructor call.

Refer this code and kindly see output,

Class A{
  A(){
        System.out.println("A-Default");
  }
  A(String msg){
     System.out.println("A-With one Argument msg : " + msg );
  }
}
public Class B extends A{
    B(){
             super("Hi");  
             System.out.println("B-Default");
    }

    public static void main(String [] args){
          new B();
    }

}

Output : 

A-With one Argument msg : Hi
B-Default