overloading with generic arguments

Hendrik Maryns <hendrik_maryns@despammed.com>
Tue, 09 Jan 2007 12:25:30 +0100
Hash: SHA1


I have a complicated question about overloading with generic arguments.
 I could not find a satisfying answer in Angelika Langer???s generics FAQ
(http://www.angelikalanger.com/GenericsFAQ/JavaGenericsFAQ.html), or in
Sun???s generics tutorial
(http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf). I hope
someone here can read better than me.

I have a class which implements a DAG with labelled edges (actually an
MDD). Recently, I decided I needed non-determinism, so multiple edges
starting from one node can have the same label. This also requires the
possibility of there being more than one root (this will occur due to
certain manipulations of the DAG, such as removing a certain layer,
which can be the root layer).

This is implemented by Nodes which have children and so on. These are
inner classes and interfaces of a wrapping class, which stores the root
and offers manipulations of the DAG. This class used to have the
following simple layout:

public class CompactFunction {

    private Node root;

    public CompactFunction(Node root){
        this.root = root;

    public CompactFunction(BidiNode root){
        this.root = root.getUnidirNode();

    public CompactFunction removeVariable(int index) {...}

    // more functions for manipulating and evaluating the function.

    public interface Node {
        // methods for all nodes

    public class NonTerminalNode {
        // nodes which have children, with methods to manipulate // the children

    public class TerminalNode {
        // nodes which have no children, but store a value

BidiNode is a node which also points up to its parents, and is used in
the construction of the DAG. Once it is constructed, I want to remove
the now no longer relevant information of the up-pointers, which is done
in the method getUnidirNode().

Now introducing nondeterminism seems simple: change root into a set of
nodes, alter the constructors and make all methods loop through the set
of nodes, as necessary. The problem is the second point; with the
following declaration:

    CompactFunction(Set<BidiNode> roots) {
        for (NonTerminalBidiNode root : roots) {

    CompactFunction(Set<Node> roots) {

Eclipse gives me the following errors:

Duplicate method CompactFunction(Set<CompactFunctionBuilder.BidiNode>)
in type CompactFunction

for the first constructor, and

Duplicate method CompactFunction(Set<CompactFunction.Node>) in type

for the second one. I suppose this is because erasure makes the method
signatures the same, but I thought overloading was handled by the
compiler, so this should work fine, right?

So the question: are these error messages correct, and if yes, what is
an alternative solution to achieve my goal?

Thanks for reading this far,
- --
Hendrik Maryns
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