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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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package org.aspectj.apache.bcel.generic;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact [email protected].
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache BCEL", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * .
 */

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import org.aspectj.apache.bcel.classfile.Utility;

/**
 * Instances of this class give users a handle to the instructions contained in an InstructionList. Instruction objects may be used
 * more than once within a list, this is useful because it saves memory and may be much faster.
 *
 * Within an InstructionList an InstructionHandle object is wrapped around all instructions, i.e., it implements a cell in a
 * doubly-linked list. From the outside only the next and the previous instruction (handle) are accessible. One can traverse the
 * list via an Enumeration returned by InstructionList.elements().
 *
 * @version $Id: InstructionHandle.java,v 1.9 2009/10/05 17:35:36 aclement Exp $
 * @author M. Dahm
 * @see Instruction
 * @see BranchHandle
 * @see InstructionList
 */
public class InstructionHandle implements java.io.Serializable {
	InstructionHandle next, prev; // Will be set from the outside
	Instruction instruction;
	protected int pos = -1; // byte code offset of instruction
	private Set targeters = Collections.emptySet();

	protected InstructionHandle(Instruction i) {
		setInstruction(i);
	}

	static final InstructionHandle getInstructionHandle(Instruction i) {
		return new InstructionHandle(i);
	}

	public final InstructionHandle getNext() {
		return next;
	}

	public final InstructionHandle getPrev() {
		return prev;
	}

	public final Instruction getInstruction() {
		return instruction;
	}

	/**
	 * Replace current instruction contained in this handle. Old instruction is disposed using Instruction.dispose().
	 */
	public void setInstruction(Instruction i) { // Overridden in BranchHandle
		if (instruction != null) {
			instruction.dispose();
		}
		instruction = i;
	}

	/**
	 * @return the position, i.e., the byte code offset of the contained instruction. This is accurate only after
	 *         InstructionList.setPositions() has been called.
	 */
	public int getPosition() {
		return pos;
	}

	/**
	 * Set the position, i.e., the byte code offset of the contained instruction.
	 */
	void setPosition(int pos) {
		this.pos = pos;
	}

	/**
	 * Delete contents, i.e., remove user access and make handle reusable.
	 */
	// OPTIMIZE get rid of this? why do we need it
	void dispose() {
		next = prev = null;
		instruction.dispose();
		instruction = null;
		pos = -1;
		removeAllTargeters();
	}

	/**
	 * Remove all targeters, if any.
	 */
	public void removeAllTargeters() {
		targeters.clear();
	}

	/**
	 * Denote this handle isn't referenced anymore by t.
	 */
	public void removeTargeter(InstructionTargeter t) {
		targeters.remove(t);
	}

	/**
	 * Denote this handle is being referenced by t.
	 */
	public void addTargeter(InstructionTargeter t) {
		if (targeters == Collections.EMPTY_SET) {
			targeters = new HashSet<>();
		}
		targeters.add(t);
	}

	public boolean hasTargeters() {
		return !targeters.isEmpty();
	}

	public Set getTargeters() {
		return targeters;
	}

	public Set getTargetersCopy() {
		Set copy = new HashSet<>(targeters);
		return copy;
	}

	/**
	 * @return a (verbose) string representation of the contained instruction.
	 */
	public String toString(boolean verbose) {
		return Utility.format(pos, 4, false, ' ') + ": " + instruction.toString(verbose);
	}

	public String toString() {
		return toString(true);
	}

}




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