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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.io.DataOutputStream;
import java.io.IOException;

import org.aspectj.apache.bcel.util.ByteSequence;

/**
 * Select - Abstract super class for LOOKUPSWITCH and TABLESWITCH instructions.
 *
 * @version $Id: InstructionSelect.java,v 1.4 2009/10/05 17:35:36 aclement Exp $
 * @author M. Dahm
 * @see LOOKUPSWITCH
 * @see TABLESWITCH
 * @see InstructionList
 */
public abstract class InstructionSelect extends InstructionBranch {
	protected int[] match; // matches, i.e., case 1: ...
	protected int[] indices; // target offsets
	protected InstructionHandle[] targets; // target objects in instruction list
	protected int fixedLength; // fixed length defined by subclasses
	protected int matchLength; // number of cases
	protected int padding = 0; // number of pad bytes for alignment

	protected short length;

	/**
	 * (Match, target) pairs for switch. `Match' and `targets' must have the same length of course.
	 *
	 * @param match array of matching values
	 * @param targets instruction targets
	 * @param target default instruction target
	 */
	InstructionSelect(short opcode, int[] match, InstructionHandle[] targets, InstructionHandle target) {
		super(opcode, target);

		this.targets = targets;
		for (InstructionHandle instructionHandle : targets) {
			notifyTarget(null, instructionHandle, this);
		}

		this.match = match;

		if ((matchLength = match.length) != targets.length) {
			throw new ClassGenException("Match and target array have not the same length");
		}

		indices = new int[matchLength];
	}

	protected int getTargetOffset(InstructionHandle target) {
		if (target == null) {
			throw new ClassGenException("Target of " + super.toString(true) + " is invalid null handle");
		}

		int t = target.getPosition();

		if (t < 0) {
			throw new ClassGenException("Invalid branch target position offset for " + super.toString(true) + ":" + t + ":"
					+ target);
		}

		return t - positionOfThisInstruction;
	}

	/**
	 * Since this is a variable length instruction, it may shift the following instructions which then need to update their
	 * position.
	 *
	 * 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) {
		positionOfThisInstruction += offset; // Additional offset caused by
		// preceding SWITCHs, GOTOs,
		// etc.

		short old_length = length;

		/*
		 * Alignment on 4-byte-boundary, + 1, because of tag byte.
		 */
		padding = (4 - (positionOfThisInstruction + 1) % 4) % 4;
		length = (short) (fixedLength + padding); // Update length

		return length - old_length;
	}

	/**
	 * Dump instruction as byte code to stream out.
	 *
	 * @param out Output stream
	 */
	public void dump(DataOutputStream out) throws IOException {
		out.writeByte(opcode);

		for (int i = 0; i < padding; i++) {
			out.writeByte(0);
		}

		targetIndex = getTargetOffset(); // Write default target offset
		out.writeInt(targetIndex);
	}

	public InstructionSelect(short opcode, ByteSequence bytes) throws IOException {
		super(opcode);
		padding = (4 - bytes.getIndex() % 4) % 4; // Compute number of pad bytes

		for (int i = 0; i < padding; i++) {
			bytes.readByte();
		}

		// Default branch target common for both cases (TABLESWITCH,
		// LOOKUPSWITCH)
		targetIndex = bytes.readInt();
	}

	/**
	 * @return mnemonic for instruction
	 */
	public String toString(boolean verbose) {
		StringBuilder buf = new StringBuilder(super.toString(verbose));

		if (verbose) {
			for (int i = 0; i < matchLength; i++) {
				String s = "null";

				if (targets[i] != null) {
					s = targets[i].getInstruction().toString();
				}

				buf.append("(" + match[i] + ", " + s + " = {" + indices[i] + "})");
			}
		} else {
			buf.append(" ...");
		}

		return buf.toString();
	}

	/**
	 * Set branch target for `i'th case
	 */
	public void setTarget(int i, InstructionHandle target) {
		notifyTarget(targets[i], target, this);
		targets[i] = target;
	}

	/**
	 * @param old_ih old target
	 * @param new_ih new target
	 */
	public void updateTarget(InstructionHandle old_ih, InstructionHandle new_ih) {
		boolean targeted = false;

		if (targetInstruction == old_ih) {
			targeted = true;
			setTarget(new_ih);
		}

		for (int i = 0; i < targets.length; i++) {
			if (targets[i] == old_ih) {
				targeted = true;
				setTarget(i, new_ih);
			}
		}

		if (!targeted) {
			throw new ClassGenException("Not targeting " + old_ih);
		}
	}

	/**
	 * @return true, if ih is target of this instruction
	 */
	public boolean containsTarget(InstructionHandle ih) {
		if (targetInstruction == ih) {
			return true;
		}

		for (InstructionHandle target : targets) {
			if (target == ih) {
				return true;
			}
		}

		return false;
	}

	/**
	 * Inform targets that they're not targeted anymore.
	 */
	void dispose() {
		super.dispose();

		for (InstructionHandle target : targets) {
			target.removeTargeter(this);
		}
	}

	/**
	 * @return array of match indices
	 */
	public int[] getMatchs() {
		return match;
	}

	/**
	 * @return array of match target offsets
	 */
	public int[] getIndices() {
		return indices;
	}

	public boolean equals(Object other) {
		return this == other;
	}

	public int hashCode() {
		return opcode * 37;
	}

	/**
	 * @return array of match targets
	 */
	public InstructionHandle[] getTargets() {
		return targets;
	}

	public int getLength() {
		return length;
	}
}