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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) 2004, 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 - Initial API and implementation
 *     James Blackburn (Broadcom Corp.) - ongoing development
 *     Lars Vogel  - Bug 473427
 *******************************************************************************/
package org.eclipse.core.internal.utils;

import java.util.HashMap;

/**
 * A string pool is used for sharing strings in a way that eliminates duplicate
 * equal strings.  A string pool instance can be maintained over a long period
 * of time, or used as a temporary structure during a string sharing pass over
 * a data structure.
 * 
 * This class is not intended to be subclassed by clients.
 * 
 *
 * @see IStringPoolParticipant
 * @since 3.1
 */
public final class StringPool {
	private int savings;
	private final HashMap map = new HashMap<>();

	/**
	 * Creates a new string pool.
	 */
	public StringPool() {
		super();
	}

	/**
	 * Adds a String to the pool.  Returns a String
	 * that is equal to the argument but that is unique within this pool.
	 * @param string The string to add to the pool
	 * @return A string that is equal to the argument.
	 */
	public String add(String string) {
		if (string == null)
			return string;
		String result = map.putIfAbsent(string, string);
		if (result != null) {
			if (result != string) {
				// XXX that number is wrong since String implementation changed to LATIN1
				// encoding, also interned String may have become externed:
				savings += 44 + 2 * string.length();
			}
			return result;
		}
		return string;
	}

	/**
	 * Returns an estimate of the size in bytes that was saved by sharing strings in
	 * the pool.  In particular, this returns the size of all strings that were added to the
	 * pool after an equal string had already been added.  This value can be used
	 * to estimate the effectiveness of a string sharing operation, in order to
	 * determine if or when it should be performed again.
	 *
	 * In some cases this does not precisely represent the number of bytes that
	 * were saved.  For example, say the pool already contains string S1.  Now
	 * string S2, which is equal to S1 but not identical, is added to the pool five
	 * times. This method will return the size of string S2 multiplied by the
	 * number of times it was added, even though the actual savings in this case
	 * is only the size of a single copy of S2.
	 */
	public int getSavedStringCount() {
		return savings;
	}
}