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The AspectJ weaver applies aspects to Java classes. It can be used as a Java agent in order to apply load-time weaving (LTW) during class-loading and also contains the AspectJ runtime classes.
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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 (https://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
 * .
 */

/**
 * BranchHandle is returned by specialized InstructionList.append() whenever a BranchInstruction is appended. This is useful when
 * the target of this instruction is not known at time of creation and must be set later via setTarget().
 *
 * @see InstructionHandle
 * @see Instruction
 * @see InstructionList
 * @version $Id: BranchHandle.java,v 1.5 2009/10/05 17:35:36 aclement Exp $
 * @author M. Dahm
 */
public final class BranchHandle extends InstructionHandle {
	private InstructionBranch bi; // An alias in fact, but saves lots of casts

	private BranchHandle(InstructionBranch i) {
		super(i);
		bi = i;
	}

	static final BranchHandle getBranchHandle(InstructionBranch i) {
		return new BranchHandle(i);
	}

	/*
	 * Override InstructionHandle methods: delegate to branch instruction. Through this overriding all access to the private
	 * i_position field should be prevented.
	 */
	public int getPosition() {
		return bi.positionOfThisInstruction;
	}

	void setPosition(int pos) {
		this.pos = bi.positionOfThisInstruction = pos;
	}

	/**
	 * Called by InstructionList.setPositions when setting the position for every instruction. In the presence of variable length
	 * instructions 'setPositions()' performs multiple passes over the instruction list to calculate the correct (byte) positions
	 * and offsets by calling this function.
	 *
	 * @param offset additional offset caused by preceding (variable length) instructions
	 * @param max_offset the maximum offset that may be caused by these instructions
	 * @return additional offset caused by possible change of this instruction's length
	 */
	protected int updatePosition(int offset, int max_offset) {
		int x = bi.updatePosition(offset, max_offset);
		pos = bi.positionOfThisInstruction;
		return x;
	}

	/**
	 * Pass new target to instruction.
	 */
	public void setTarget(InstructionHandle ih) {
		bi.setTarget(ih);
	}

	/**
	 * Update target of instruction.
	 */
	public void updateTarget(InstructionHandle old_ih, InstructionHandle new_ih) {
		bi.updateTarget(old_ih, new_ih);
	}

	/**
	 * @return target of instruction.
	 */
	public InstructionHandle getTarget() {
		return bi.getTarget();
	}

	/**
	 * Set new contents. Old instruction is disposed and may not be used anymore.
	 */
	public void setInstruction(Instruction i) {
		super.setInstruction(i);
		bi = (InstructionBranch) i;
	}
}