gistfile1.java

    public interface MyInterface<T extends MyInterface> {
        T someMethod();
    }

    public class FirstWidget implements MyInterface<FirstWidget> {
        public FirstWidget someMethod() {
            return this;
        }
    }

    public class SecondWidget implements MyInterface<SecondWidget> {
        public SecondWidget someMethod() {
            return this;
        }
    }


    public class Demo {
        public void someMethod(FirstWidget w) {
            // the compiler knows that someMethod() will return a FirstWidget...
            FirstWidget fw = w.someMethod();
        }
    }