Question

I try to do this:

public class Demo{
public Demo() {
    Demo(null)
}
public Demo(Interface myI) {
    ...
}
}

I would like the Demo() constructor to call the Demo(Interface) constructor with null however eclipse complains “Demo(null) is undefined” on the line where I call Demo(null). What do I have to change?

Answer 1

You are trying to call a method called Demo which you haven’t defined.

e.g.

class A {
   public A() {
      this(1); // calls constructor A(int)
      A(1); // calls method A(int)
   }
   public A(int i) {} // constructor A(int)
   public void A(int i) {} // method A(int)

   public A A(A a) { return a; } // method A(A) which returns A
}

If you want a constructor to call another you need to use this() like

public Demo() {
    this(null);
}