Can a java method implementing a base class method return an inherited class?

Question

Let's say I have the standard Draw class with inherited classes of Circle and Square. Is there a way to do the following? Maybe with generics?

class Draw {
  public abstract Draw duplicate();
}

class Circle extends Draw {
  public Circle duplicate() {
    return new Circle();
  }
}

class Square extends Draw {
  public Square duplicate() {
    return new Square();
  }
}

Answer 1

Yes, it is possible to have an overriding method return a type that is a subclass of the superclass method's return type. This technique, called "covariant return types", is described at the bottom of a Java tutorial on return types. This works because a Circle and a Square are Draws, so even if you have a superclass reference, and you don't know or care which subclass you really have, you still are guaranteed to get back a Draw.

Incidentally, to get your code to compile, you just need to make the Draw class abstract. Everything else, including the covariant return types, looks fine.

Answer 2

Yes, you can since Java 5.

Since Java 5, a method in a subclass may return an object whose type is a subclass of the type returned by the method with the same signature in the superclass. (source). This is called covariant return types.