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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/*******************************************************************************
 * 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.
 */
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);
	}
}