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Java example source code file (Select.java)

This example Java source code file (Select.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

branchinstruction, classgenexception, compute, gotos, instructionhandle, ioexception, not, override, padding, select, stackproducer, string, update, write

The Select.java Java example source code

/*
 * reserved comment block
 * DO NOT REMOVE OR ALTER!
 */
package com.sun.org.apache.bcel.internal.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 apache@apache.org.
 *
 * 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
 * <http://www.apache.org/>.
 */
import java.io.*;
import com.sun.org.apache.bcel.internal.util.ByteSequence;

/**
 * Select - Abstract super class for LOOKUPSWITCH and TABLESWITCH instructions.
 *
 * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm
 * @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++) {
      BranchInstruction.notifyTargetChanged(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
   */
  @Override
  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
   */
  @Override
  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.
   */
  @Override
  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
   */
  @Override
  public String toString(boolean verbose) {
    final StringBuilder buf = new StringBuilder(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("(").append(match[i]).append(", ")
             .append(s).append(" = {").append(indices[i]).append("})");
      }
    }
    else
      buf.append(" ...");

    return buf.toString();
  }

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

  /**
   * @param old_ih old target
   * @param new_ih new target
   */
  @Override
  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
   */
  @Override
  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.
   */
  @Override
  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; }
}

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