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
path = null;
		}
        if (parent != null) {
            if (equals(parent, getRoot())) {
				return super.getRawChildren(parent);
			}
            IContentProvider cp = getContentProvider();
             if (cp instanceof ITreePathContentProvider) {
    			ITreePathContentProvider tpcp = (ITreePathContentProvider) cp;
    			if (path == null) {
    				
    				Widget w = findItem(parent);
    				if (w instanceof Item) {
    					Item item = (Item) w;
    					path = getTreePathFromItem(item);
    				}
    				if (path == null) {
    					path = new TreePath(new Object[] { parent });
    				}
    			}
    			Object[] result = tpcp.getChildren(path);
                if (result != null) {
					return result;
				}
    		} else if (cp instanceof ITreeContentProvider) {
    			ITreeContentProvider tcp = (ITreeContentProvider) cp;
                Object[] result = tcp.getChildren(parent);
                if (result != null) {
					return result;
				}