WeakArrayList.java

public class WeakArrayList<E> extends AbstractList<E>
{
	private List<WeakReference<E>> backingList = new ArrayList<>();

	@Override
	public E get(int index)
	{
		clean();
		WeakReference<E> obj = backingList.get(index);
		return obj != null ? obj.get() : null;
	}

	@Override
	public E set(int index, E element)
	{
		clean();
		WeakReference<E> ret = backingList.set(index, new WeakReference<>(element));
		return ret != null ? ret.get() : null;
	}

	@Override
	public void add(int index, E element)
	{
		backingList.add(index, new WeakReference<>(element));
	}

	@Override
	public boolean remove(Object o)
	{
		if (backingList.isEmpty()) return false;
		for (Iterator<WeakReference<E>> iter = backingList.iterator(); iter.hasNext();)
		{
			WeakReference<E> ref = iter.next();
			if (ref.get() == null || ref.get().equals(o))
			{
				iter.remove();
				return true;
			}
		}
		return false;
	}
	
	@Override
	public boolean contains(Object o)
	{
		if (backingList.isEmpty()) return false;
		for (Iterator<WeakReference<E>> iter = backingList.iterator(); iter.hasNext();)
		{
			WeakReference<E> ref = iter.next();
			if (ref.get() == null)
			{
				iter.remove();
				return false;
			}
			else if(ref.get().equals(o)) return true;
		}
		return false;
	}
	
	@Override
	public int indexOf(Object o)
	{
		if (backingList.isEmpty()) return -1;
		for (ListIterator<WeakReference<E>> listIter = backingList.listIterator(); listIter.hasNext();)
		{
			WeakReference<E> ref = listIter.next();
			if (ref.get() == null) listIter.remove();
			else if(ref.get().equals(o)) return listIter.nextIndex() - 1;
		}
		return -1;
	}
	
	@Override
	public int lastIndexOf(Object o)
	{
		if (backingList.isEmpty()) return -1;
		int index = -1;
		for (ListIterator<WeakReference<E>> listIter = backingList.listIterator(); listIter.hasNext();)
		{
			WeakReference<E> ref = listIter.next();
			if (ref.get() == null) listIter.remove();
			else if(ref.get().equals(o)) index = listIter.nextIndex() - 1;
		}
		return index;
	}

	@Override
	public int size()
	{
		return backingList.size();
	}
	
	private void clean()
	{
		for (Iterator<WeakReference<E>> iter = backingList.iterator(); iter.hasNext();)
		{
			WeakReference<E> ref = iter.next();
			if(ref.get() == null) iter.remove(); 
		}
	}
}