| /******************************************************************************* |
| * Copyright (c) 2000, 2015 IBM Corporation and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| package org.eclipse.core.internal.watson; |
| |
| /** |
| * This is what you would expect for an element tree comparator. |
| * Clients of the element tree that want specific comparison behaviour |
| * must define their own element comparator (without subclassing or |
| * otherwise extending this comparator). Internal element tree operations |
| * rely on the behaviour of this type, and the ElementTree maintainer |
| * reserves the right to change its behaviour as necessary. |
| */ |
| public final class DefaultElementComparator implements IElementComparator { |
| private static DefaultElementComparator singleton; |
| |
| /** |
| * Force clients to use the singleton |
| */ |
| protected DefaultElementComparator() { |
| super(); |
| } |
| |
| /** |
| * Returns the type of change. |
| */ |
| @Override |
| public int compare(Object oldInfo, Object newInfo) { |
| if (oldInfo == null && newInfo == null) |
| return 0; |
| if (oldInfo == null || newInfo == null) |
| return 1; |
| return testEquality(oldInfo, newInfo) ? 0 : 1; |
| } |
| |
| /** |
| * Returns the singleton instance |
| */ |
| public static IElementComparator getComparator() { |
| if (singleton == null) { |
| singleton = new DefaultElementComparator(); |
| } |
| return singleton; |
| } |
| |
| /** |
| * Makes a comparison based on equality |
| */ |
| protected boolean testEquality(Object oldInfo, Object newInfo) { |
| if (oldInfo == null && newInfo == null) |
| return true; |
| if (oldInfo == null || newInfo == null) |
| return false; |
| |
| return oldInfo.equals(newInfo); |
| } |
| } |