Re: Detailed Java Generics

I have a very detailed/complicated java generics question. Consider
the following code

public abstract class AEdge {
    ANode fr, to;
}

public abstract class ANode { }

public class CEdge extends AEdge { }

public class CNode extends ANode { }

public class MyEdgeDatabase<N extends ANode, E extends AEdge> {
    Set<E> edges;

    public abstract class ForEachEdgeFrom {
        public ForEachEdgeFrom(N n) {
            for(E e : edges) if (e.fr == n) run(e);
        }
        public abstract void run(E e);
    }
}

public class Test {
    MyEdgeDatabase<CNode, CEdge> edgeDB
        = new MyEdgeDatabase<CNode, CEdge>();
    CNode n = new CNode();

    public void doIt() {
        edgeDB.new ForEachEdgeFrom(n){
            public void run(CEdge e) {
                System.out.println(e);
            }
        };
    }
}

The doIt() method will not compile. It gives the following error:

"No enclosing instance of type MyEdgeDatabase<N,E> is accessible. Must
qualify the allocation with an enclosing instance of type
MyEdgeDatabase<N,E> (e.g. x.new A() where x is an instance of
MyEdgeDatabase<N,E>)."