Re: Collection Issue

Thu, 25 Sep 2008 12:56:21 -0700 (PDT)
On Sep 25, 1:35 pm, Mark Space <> wrote: wrote:

I have 2 Collections.
One of them has only one element that I want removed from the other.
Naturally I do:


I keep getting null position pointer.
So I copy the java utils code and modify it a bit and realise that the
problem lies in the "contains()" code.
When I check for equality of the element in listB to be removed from
listA with "==", it returns "true".
But when I check with ".equals()" it returns false.
This is flabbergasting to me. To my knowledge, "==" checks to see if
the Objects are at the same address. If that is true, how on earth
could ANYTHING about them be different?

So, "equals()" is a method that anyone can override. Obviously, someone
did override it, and botched the job. (Or your class derives from a
class that overrides the equals() method.)

What is the list element that you are dealing with here? Can we have a
look at its code?


public class RemoteEventListenerList<T extends RemoteEventListener>
        InvocationHandler {
    private List<T> list = new LinkedList<T>();
    private List<T> toAdd = new ArrayList<T>();
    private final Class<T> type;
    private T proxy = null;
    private List<T> toRemove = new ArrayList<T>();

    public RemoteEventListenerList(Class<T> type) {
        this.type = type;

    public Object invoke(Object o, Method method, Object[] args)
            throws Throwable {
        dispatchList(list, method, args);
        while (moreAdded()) {
            final List<T> temp = new ArrayList<T>(toAdd);
            dispatchList(temp, method, args);
        return null;

    private void updateList() {

    private boolean moreAdded() {
        return !toAdd.isEmpty();

    private void dispatchList(List<T> dispList, Method method,
Object[] args)
            throws IllegalAccessException {
        for (Object t : dispList.toArray()) {
            dispatch(method, type.cast(t), args);

    private synchronized void doRemove() {
        removeAll(list, toRemove);
        //removeAll(list, toRemove);

    private void doAdd() {

    public void removeAll(List<T> l, List<T> c) {
        Iterator<T> e = l.iterator();
        while (e.hasNext()) {
            if (contains(l, {//when it reaches the element,
it throws a null exception
                e.remove(); // even though it DOES contain

// I was experimenting here.

    public void removeAll(List<T> l, List<T> c) {
        for (T e: l) {
            if (contains(l, e)) {

    public boolean contains(List<T> c, T l) {
        for (T e: c) {
            if (e == l) return true;
        return false;

    private void dispatch(Method method, T t, Object[] args)
            throws IllegalAccessException {
        try {
            method.invoke(t, args);
        } catch (InvocationTargetException e) {
            if (!(e.getTargetException() instanceof
DisconnectedException)) {
            } else {
        } catch (RuntimeException e) {

    public T getProxy() {
        if (proxy == null) {
            proxy = type.cast(Proxy
                    .newProxyInstance(type.getClassLoader(), new
Class[]{type}, this)
        return proxy;

    public void add(T t) {

    private void remove(T t) {

    public void removeToAdd(T t) {
        remove(t); // I added this later, not sure about it


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