Bug 32254 [Viewers] AbstractTreeViewer uses HashSet to remember expansion state
I20030216 The custom hash table should be used instead. Otherwise expansion state may be lost due to a different equals implementation of the element and the IElementComparer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
childItem.dispose();
			}
		}
		Control tree = getControl();
		for (Iterator i = parentItems.iterator(); i.hasNext();) {
			Item parentItem = (Item) i.next();
			if (!getExpanded(parentItem) && getItemCount(parentItem) == 0) {
				
				if (isExpandable(parentItem.getData())) {
					newItem(parentItem, SWT.NULL, -1);
				} else {
					
					tree.redraw();
				}
			}
		}
	}
	/**
	 * Sets the expanded state of all items to correspond to the given set of
	 * expanded elements.
	 * 
	 * @param expandedElements
	 *           the set (element type: <code>Object</code>) of elements
	 *           which are expanded
	 * @param widget
	 *           the widget
	 */
	private void internalSetExpanded(HashSet expandedElements, Widget widget) {
		Item[] items = getChildren(widget);
		for (int i = 0; i < items.length; i++) {