--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/platform35/org.eclipse.core.resources/src/org/eclipse/core/internal/watson/DefaultElementComparator.java	Thu Jul 30 11:56:23 2009 -0500
@@ -0,0 +1,63 @@
+/*******************************************************************************
+ * Copyright (c) 2000, 2005 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.
+	 */
+	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);
+	}
+}