Enforcing return type for an class that implements an interface

Question

How do I enforce that the method getFoo() in the implementing class, returns a list of the type of same implementing class.

public interface Bar{
     ....
          


        

Answer 1

How about this:

interface Bar
{
    // everything but getFoo ( ) ;
}

interface FooGetter < T >
{
    List < ? extends T > getFoo ( ) ;
}

interface BarRef < T extends Bar & FooGetter < T > >
{
    T get ( ) ;
}

anything that implements BarRef must implement T and anything that implements T must have the appropriately enforced getFoo method.