Java APIs

Hello. I am writing a new concrete implementation of the Set interface, using the source code from java.util.TreeSet as a rough guide to the way I should lay my code out. Having completed the code, I compiled only to get the following error message from the compiler:

C:\ ... \ArraySet.java:7: name clash: add(E) in ArraySet<E> and add(E) in java.util.Set have the same erasure, yet neither overrides the other
public class ArraySet<E>

Here is some of my source code:

import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class ArraySet<E>
	extends AbstractSet
	implements Cloneable/*, java.io.Serializable*/ {

	private transient ArrayList<E> list;

	public ArraySet() {
		list = new ArrayList<E>();
	}

	public ArraySet(Collection<? extends E> c) {
		this();
		addAll(c);
	}

	public Iterator<E> iterator() {
		return list.iterator();
	}

	public int size() {
		return list.size();
	}

	public boolean isEmpty() {
		return list.isEmpty();
	}

	public boolean contains(Object o) {
		return list.contains(o);
	}

	public boolean add(E o) {
		if (!list.contains(o))
			return list.add( o );
		return false;
	}

	public void add(int index, E o) {
		if (!list.contains(o))
			list.add( index, o );
	}
     // ... 

and here is some of the code from TreeSet (minus the comments)

public class TreeSet<E>
    extends AbstractSet<E>
    implements SortedSet<E>, Cloneable, java.io.Serializable
{
    private transient SortedMap<E,Object> m; // The backing Map
    private transient Set<E> keySet;	// The keySet view of the backing Map

    // Dummy value to associate with an Object in the backing Map
    private static final Object PRESENT = new Object();

    private TreeSet(SortedMap<E,Object> m) {
        this.m = m;
        keySet = m.keySet();
    }

    public TreeSet() {
	this(new TreeMap<E,Object>());
    }

    public TreeSet(Comparator<? super E> c) {
	this(new TreeMap<E,Object>(c));
    }

    public TreeSet(Collection<? extends E> c) {
        this();
        addAll(c);
    }

    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
	addAll(s);
    }

    public Iterator<E> iterator() {
	return keySet.iterator();
    }

    public int size() {
	return m.size();
    }

    public boolean isEmpty() {
	return m.isEmpty();
    }

    public boolean contains(Object o) {
	return m.containsKey(o);
    }

    public boolean add(E o) {
	return m.put(o, PRESENT)==null;
    }
    // ...

As far as I can tell, my source code is doing the equivalent of everything that the TreeSet code is doing, yet I get this compiler error concerning the add() method. What am I doing wrong?

Thanks in advance

frag