Generics/Comparator

Hello,

here is a short class source with begining of generics. Could you please
tell me how to use generics with the comparators ?

import java.util.Comparator;
import java.util.TreeSet;

public class TestComparator {

    private static abstract class A {
    }

    private static class B extends A {
    }

    private static class C extends A {
    }

    private static abstract class HandlerOfA {
        public abstract Comparator getComparator();
    }

    private static class HandlerOfB extends HandlerOfA {
        public static class ComparatorOfB implements Comparator<B> {
            public int compare(B b1, B b2) {
             return 0;
            }

        }
        public Comparator getComparator() {
            return new ComparatorOfB();
        }
    }

    private static class HandlerOfC extends HandlerOfA {
        public static class ComparatorOfC implements Comparator<C> {
            public int compare(C c1, C c2) {
             return 0;
            }

        }
        public Comparator getComparator() {
            return new ComparatorOfC();
        }
    }

    public static void main(String[] args) {
        HandlerOfA contA = new HandlerOfB();
        HandlerOfB contB = new HandlerOfB();
        HandlerOfC contC = new HandlerOfC();

        TreeSet<A> treesetA = new TreeSet<A>(contA.getComparator());
        treesetA.add(new B());

        TreeSet<B> treesetB = new TreeSet<B>(contB.getComparator());
        treesetB.add(new B());

        TreeSet<C> treesetC = new TreeSet<C>(contC.getComparator());
        treesetC.add(new C());

    }
}

Thanks for any help