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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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/* ====================================================================
 * 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
 * .
 */
package org.aspectj.apache.bcel.generic;

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

import org.aspectj.apache.bcel.Constants;
import org.aspectj.apache.bcel.classfile.ConstantPool;

/**
 * Abstract super class for branching instructions like GOTO, IFEQ, etc.. Branch instructions may have a variable length, namely
 * GOTO, JSR, LOOKUPSWITCH and TABLESWITCH. A branch instruction may be talking in terms of absolute destination (targetIndex) or
 * about an instruction it doesnt yet know the position if (targetInstruction). targetInstruction (if set) overrides targetIndex
 *
 * @see InstructionList
 * @version $Id: InstructionBranch.java,v 1.6 2009/10/05 17:35:36 aclement Exp $
 * @author M. Dahm
 */
public class InstructionBranch extends Instruction implements InstructionTargeter {
	private static final int UNSET = -1;

	protected int targetIndex = UNSET; // Branch target relative to this
	// instruction
	protected InstructionHandle targetInstruction; // Target object in
	// instruction list
	protected int positionOfThisInstruction; // for calculating relative branch

	// destinations!

	public InstructionBranch(short opcode, InstructionHandle target) {
		super(opcode);
		setTarget(target);
	}

	public InstructionBranch(short opcode, int index) {
		super(opcode);
		this.targetIndex = index;
	}

	public InstructionBranch(short opcode) {
		super(opcode);
	}

	public void dump(DataOutputStream out) throws IOException {
		int target = getTargetOffset();

		if (Math.abs(target) >= 32767 && opcode != GOTO_W && opcode != JSR_W) {
			throw new ClassGenException("Branch target offset too large for short.  Instruction: " + getName().toUpperCase() + "("
					+ opcode + ")");
		}

		out.writeByte(opcode);

		switch (opcode) {

		case GOTO_W:
		case JSR_W:
			out.writeInt(target);
			break;

		case IF_ACMPEQ:
		case IF_ACMPNE:
		case IF_ICMPEQ:
		case IF_ICMPGE:
		case IF_ICMPGT:
		case IF_ICMPLE:
		case IF_ICMPLT:
		case IF_ICMPNE:
		case IFEQ:
		case IFLE:
		case IFLT:
		case IFGT:
		case IFNE:
		case IFGE:
		case IFNULL:
		case IFNONNULL:
		case GOTO:
		case JSR:
			out.writeShort(target);
			break;

		default:
			throw new IllegalStateException("Don't know how to write out " + getName().toUpperCase());
		}

	}

	protected int getTargetOffset() {
		if (targetInstruction == null && targetIndex == UNSET) {
			throw new ClassGenException("Target of " + super.toString(true) + " is unknown");
		}

		if (targetInstruction == null) {
			return targetIndex;
		} else {
			return targetInstruction.getPosition() - positionOfThisInstruction;
		}
	}

	/**
	 * 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 i = getTargetOffset();

		positionOfThisInstruction += offset;

		if (Math.abs(i) >= 32767 - max_offset && opcode != JSR_W && opcode != GOTO_W) {
			// Try and promote it to wide if we can
			if (opcode == JSR || opcode == GOTO) {
				if (opcode == JSR) {
					opcode = JSR_W;
				} else {
					opcode = GOTO_W;
				}
				return 2; // instruction jump destination grows from a short to a long
			} else {
				throw new IllegalStateException("Unable to pack method, jump (with opcode=" + opcode + ") is too far: "
						+ Math.abs(i));
			}
		}

		return 0;
	}

	/**
	 * Long output format:
	 *
	 * @param verbose long/short format switch
	 * @return mnemonic for instruction
	 */
	public String toString(boolean verbose) {
		String s = super.toString(verbose);
		String t = "null";

		if (verbose) {
			if (targetInstruction != null) {
				if (targetInstruction.getInstruction() == this) {
					t = "";
				} else if (targetInstruction.getInstruction() == null) {
					t = "";
				} else {
					t = targetInstruction.getInstruction().toString(false);
				}
			}
		} else {
			if (targetInstruction != null) {
				targetIndex = getTargetOffset();
				t = "" + (targetIndex + positionOfThisInstruction);
			}
		}

		return s + " -> " + t;
	}

	/**
	 * @return target offset in byte code
	 */
	public final int getIndex() {
		return targetIndex;
	}

	/**
	 * @return target of branch instruction
	 */
	public InstructionHandle getTarget() {
		return targetInstruction;
	}

	/**
	 * Set branch target
	 *
	 * @param target branch target
	 */
	public void setTarget(InstructionHandle target) {
		notifyTarget(this.targetInstruction, target, this);
		this.targetInstruction = target;
	}

	/**
	 * Used by BranchInstruction, LocalVariableGen, CodeExceptionGen
	 */
	static final void notifyTarget(InstructionHandle oldHandle, InstructionHandle newHandle, InstructionTargeter t) {
		if (oldHandle != null) {
			oldHandle.removeTargeter(t);
		}
		if (newHandle != null) {
			newHandle.addTargeter(t);
		}
	}

	/**
	 * Update the target destination for this instruction. If an oldHandle is provided it is checked to verify that is where the
	 * target currently points to before changing it.
	 *
	 * @param oldHandle old target
	 * @param newHandle new target
	 */
	public void updateTarget(InstructionHandle oldHandle, InstructionHandle newHandle) {
		if (targetInstruction == oldHandle) {
			setTarget(newHandle);
		} else {
			throw new ClassGenException("Not targeting " + oldHandle + ", but " + targetInstruction);
		}
	}

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

	/**
	 * Inform target that it's not targeted anymore.
	 */
	void dispose() {
		setTarget(null);
		targetIndex = -1;
		positionOfThisInstruction = -1;
	}

	public Type getType(ConstantPool cp) {
		if ((Constants.instFlags[opcode] & Constants.JSR_INSTRUCTION) != 0) {
			return new ReturnaddressType(physicalSuccessor());
		}
		return super.getType(cp);
	}

	/**
	 * Returns an InstructionHandle to the physical successor of this JsrInstruction. For this method to work, this
	 * JsrInstruction object must not be shared between multiple InstructionHandle objects! Formally, there must not be
	 * InstructionHandle objects i, j where i != j and i.getInstruction() == this == j.getInstruction().
	 *
	 * @return an InstructionHandle to the "next" instruction that will be executed when RETurned from a subroutine.
	 */
	public InstructionHandle physicalSuccessor() {
		InstructionHandle ih = this.targetInstruction;

		// Rewind!
		while (ih.getPrev() != null) {
			ih = ih.getPrev();
		}

		// Find the handle for "this" JsrInstruction object.
		while (ih.getInstruction() != this) {
			ih = ih.getNext();
		}

		InstructionHandle toThis = ih;

		while (ih != null) {
			ih = ih.getNext();
			if (ih != null && ih.getInstruction() == this) {
				throw new RuntimeException("physicalSuccessor() called on a shared JsrInstruction.");
			}
		}

		// Return the physical successor
		return toThis.getNext();
	}

	public boolean isIfInstruction() {
		return (Constants.instFlags[opcode] & Constants.IF_INST) != 0;
	}

	/**
	 * Only equal if they are the same branch instruction - otherwise too risky as the targets may only temporarily be pointing at
	 * the same destination.
	 */
	public boolean equals(Object other) {
		return this == other;
	}

	public int hashCode() {
		int result = 17;
		result = opcode * 37 + result;
		return result;
	}
}