org.aspectj/bcel-builder/src/main/java/org/aspectj/apache/bcel/generic/InstructionHandle.java

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.
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 *    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.
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 * 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
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 *
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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 * 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
 * <https://www.apache.org/>.
 */

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 <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
 * @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<InstructionTargeter> 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<InstructionTargeter> getTargeters() {
		return targeters;
	}

	public Set<InstructionTargeter> getTargetersCopy() {
		Set<InstructionTargeter> 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);
	}

}