Question

Suppose I have a base class B, and a derived class D. I wish to have a method foo() within my base class that returns a new object of whatever type the instance is. So, for example, if I call B.foo() it returns an object of type B, while if I call D.foo() it returns an object of type D; meanwhile, the implementation resides solely in the base class B.

Is this possible?

Answer 1

Don’t. Make the ‘foo’ method abstract.

abstract class B {     public abstract B foo(); } 

Or receive an abstract factory through the base class constructor:

abstract class B {     private final BFactory factory;     protected B(BFactory factory) {         this.factory = factory;     }     public B foo() {         return factory.create();     } } interface BFactory {     B create(); } 

Add covariant return types and generics to taste.