Copyright (c) 2000, 2015 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2000, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * 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.
/**
 * 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
/**
	 * Force clients to use the singleton
	 */
	protected DefaultElementComparator() {
		super();
	}

	
Returns the type of change.
/**
	 * 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
/**
	 * Returns the singleton instance
	 */
	public static IElementComparator getComparator() {
		if (singleton == null) {
			singleton = new DefaultElementComparator();
		}
		return singleton;
	}

	
Makes a comparison based on equality
/**
	 * 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);
	}
}