Bug 138608 [Viewers] JFace AbstractTreeViewer: itemExists doesn't handle equal tree entries
I use a TreeViewer with - setUseHashLookup(true) - without any sorter or filter - with a comparer When I try to add an object that is equal to an existing entry in the tree, it will not be added. This is because the method private boolean itemExists(Item[] items, Object element) { if(usingElementMap()) { return findItem(element) != null; } for (int i = 0; i < items.length; i++) { if(items[i].getData().equals(element)) { return true; } } return false; } takes a shortcut if there is an element map, but the shortcut doesn't handle the 'multiple equal elements' case. There is a workaround, however: Setting a dummy sorter will avoid the call to itemExists and multiple equal elements can be added to the tree.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* 
     * @since 3.1
     */
	protected Widget internalGetWidgetToSelect(Object elementOrTreePath) {
		if(elementOrTreePath instanceof TreePath) {
			TreePath treePath = (TreePath) elementOrTreePath;
			if(treePath.getSegmentCount()==0) {
				return null;
			}
			Widget[] candidates = findItems(treePath.getLastSegment());
			for (int i = 0; i < candidates.length; i++) {
				Widget candidate = candidates[i];
				if(!(candidate instanceof Item)) {
					continue;
				}
				if(treePath.equals(getTreePathFromItem((Item) candidate), getComparer())) {
					return candidate;
				}
			}
			return null;
		}
		return findItem(elementOrTreePath);
	}
    /**
     * Recursively expands the subtree rooted at the given widget to the given
     * level.
     * <p>
     * </p>
     * Note that the default implementation of this method does not call <code>setRedraw</code>.
     *