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
int count = items.length;
        if (comparator == null) {
			return count;
		}
        int min = 0, max = count - 1;
        while (min <= max) {
            int mid = (min + max) / 2;
            Object data = items[mid].getData();
            int compare = internalCompare(comparator, parentPath, data, element);
            if (compare == 0) {
                
                while (compare == 0) {
                    ++mid;
                    if (mid >= count) {
                        break;
                    }
                    data = items[mid].getData();
                    compare = internalCompare(comparator, parentPath, data, element);
                }
                return mid;
            }
            if (compare < 0) {
				min = mid + 1;
			} else {
				max = mid - 1;
			}
        }
        return min;
    }
    /**