select.java

Java Bytecode Editor 是一个 JAVA 的字节码反汇编和修改器。它可以很方便的修改已经编译成 Class 文件的 JAVA 文件。

package org.apache.bcel.generic;

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import java.io.*;
import org.apache.bcel.util.ByteSequence;

/**
 * Select - Abstract super class for LOOKUPSWITCH and TABLESWITCH instructions.
 * 
 * @version $Id: Select.java,v 1.4 2006/03/29 10:28:43 andos Exp $
 * @author <A HREF="mailto:[e-mail]">M. Dahm</A> Modified by Ando Saabas
 * @see LOOKUPSWITCH
 * @see TABLESWITCH
 * @see InstructionList
 */
public abstract class Select extends BranchInstruction implements
		VariableLengthInstruction, StackProducer {
	protected int[] match; // matches, i.e., case 1: ...
	protected int[] indices; // target offsets
	protected InstructionHandle[] targets; // target objects in instruction
											// list
	protected int fixed_length; // fixed length defined by subclasses
	protected int match_length; // number of cases
	protected int padding = 0; // number of pad bytes for alignment

	/**
	 * Empty constructor needed for the Class.newInstance() statement in
	 * Instruction.readInstruction(). Not to be used otherwise.
	 */
	Select() {
	}

	/**
	 * (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
	 */
	Select(short opcode, int[] match, InstructionHandle[] targets,
			InstructionHandle target) {
		super(opcode, target);

		this.targets = targets;
		for (int i = 0; i < targets.length; i++)
			notifyTarget(null, targets[i], this);

		this.match = match;

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

		indices = new int[match_length];
	}

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

	public void setMatchesTargets(int[] match, InstructionHandle[] targets) {
		this.targets = targets;
		for (int i = 0; i < targets.length; i++)
			notifyTarget(null, targets[i], this);

		this.match = match;

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

		indices = new int[match_length];
	}

	/**
	 * 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) {
		position += 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 - ((position + 1) % 4)) % 4;
		length = (short) (fixed_length + 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++)
			// Padding bytes
			out.writeByte(0);

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

	/**
	 * Read needed data (e.g. index) from file.
	 */
	protected void initFromFile(ByteSequence bytes, boolean wide)
			throws IOException {
		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)
		index = bytes.readInt();
	}

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

		if (verbose) {
			for (int i = 0; i < match_length; 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;
	}

	/**
	 * Set branch target for `i'th case
	 */
	public void setDefaultTarget(InstructionHandle target) {
		super.setTarget(target);
	}

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

		if (target == 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 (target == ih)
			return true;

		for (int i = 0; i < targets.length; i++)
			if (targets[i] == ih)
				return true;

		return false;
	}

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

		for (int i = 0; i < targets.length; i++)
			targets[i].removeTargeter(this);
	}

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

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

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