How to call the constructor of an Abstract class from another constructor inside the same class (method overloading)

Question

I am extending the API of a class that I am working on and would like to make it backward compatible - so that it doesn't break any existing users of the class. I have created the new functionality by adding a new parameter to the constructor.

So that I don't repeat code (I could copy-paste code from the old constructor into the new) I would like to change the existing constructor to call the new constructor passing 0 as the default for the new parameter but I am getting a compilation error, method call expected.

Is what I am trying to do not possible (method overloading is not supported?) or am missing something?

To help show what I mean, please see the simple example below,

public abstract class AbstractCalculator {

     int result;

     // new parameter being added 
     public AbstractCalculator(int a, int b){
         result = a + b;
     }

     // existing functionality       
     public AbstractCalculator(int a){
         //compilation error here - Method call expected
         AbstractCalculator(a, 0);
     }
}

public class Calculator extends AbstractCalculator{

     public Calculator(int a){
         super(a);
     }

     public static void main(String args []){

         Calculator calc = new Calculator(4);
         System.out.println(calc.getResult());

     }    
}

AbstractCalculator(a, 0) replace with this(a, 0); – Dmitri Algazin Oct 18 '19 at 11:17 — Dmitri Algazin, Oct 18 '19 at 11:17

score 2 · Accepted Answer · answered Oct 18 '19 at 11:18

2

// existing functionality       
public AbstractCalculator(int a){
    this(a, 0);
}

answered Oct 18 '19 at 11:18

Maurice Perry

9,261
2
12
24

yep thats it - thank you. – robbie70 Oct 18 '19 at 11:20

How to call the constructor of an Abstract class from another constructor inside the same class (method overloading)

1 Answers1