Force toString() implementation in subclasses

Question

I have an abstract parent class, and I would like it to force all subclasses to implement toString() method.

However putting:

public abstract String toString();

is causing a compilation error:

Repetitive method name/signature for method 'java.lang.String toString()' in class ...

I believe this might be caused by groovy already having toString defined.

Thanks

Answer 1

This works for me. Is this new or did others just miss it?

public abstract class Filterable
{
  @Override
  public abstract String toString();
}

public class ABC extends Filterable
{
  // Won't compile without toString();
}

Answer 2

The toString() is part of the java.lang.Object class which already has a default implementation for it. So you essentially can't force the sub-classes to implement it. If you want to force this kind of behavior (not sure why) then you can do something like below

public class abstract SuperClass {
  public abstract String myToString();

  public String toString() {
    return myToString();
  }
}