ldc.java

该开源工具主要用于class文件的操作

package org.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 [e-mail].
 *
 * 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 org.apache.bcel.util.ByteSequence;

/** 
 * LDC - Push item from constant pool.
 *
 * <PRE>Stack: ... -&gt; ..., item</PRE>
 *
 * @version $Id: LDC.java,v 1.1.1.1 2001/10/29 20:00:21 jvanzyl Exp $
 * @author  <A HREF="mailto:[e-mail]">M. Dahm</A>
 */
public class LDC extends CPInstruction
  implements PushInstruction, ExceptionThrower, TypedInstruction {
  /**
   * Empty constructor needed for the Class.newInstance() statement in
   * Instruction.readInstruction(). Not to be used otherwise.
   */
  LDC() {}

  public LDC(int index) {
    super(org.apache.bcel.Constants.LDC_W, index);
    setSize();
  }
  
  // Adjust to proper size
  protected final void setSize() {
    if(index <= org.apache.bcel.Constants.MAX_BYTE) { // Fits in one byte?
      opcode = org.apache.bcel.Constants.LDC;
      length = 2;
    } else {
      opcode = org.apache.bcel.Constants.LDC_W;
      length = 3;
    }
  }

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

    if(length == 2)
      out.writeByte(index);
    else // Applies for LDC_W
      out.writeShort(index);
  }

  /**
   * Set the index to constant pool and adjust size.
   */
  public final void setIndex(int index) { 
    super.setIndex(index);
    setSize();
  }

  /**
   * Read needed data (e.g. index) from file.
   */
  protected void initFromFile(ByteSequence bytes, boolean wide)
       throws IOException
  {
    length = 2;
    index  = bytes.readUnsignedByte();
  }

  public Object getValue(ConstantPoolGen cpg) {
    org.apache.bcel.classfile.Constant c = cpg.getConstantPool().getConstant(index);

    switch(c.getTag()) {
      case org.apache.bcel.Constants.CONSTANT_String:
	int i = ((org.apache.bcel.classfile.ConstantString)c).getStringIndex();
	c = cpg.getConstantPool().getConstant(i);
	return ((org.apache.bcel.classfile.ConstantUtf8)c).getBytes();

    case org.apache.bcel.Constants.CONSTANT_Float:
	return new Float(((org.apache.bcel.classfile.ConstantFloat)c).getBytes());

    case org.apache.bcel.Constants.CONSTANT_Integer:
	return new Integer(((org.apache.bcel.classfile.ConstantInteger)c).getBytes());

    default: // Never reached
      throw new RuntimeException("Unknown or invalid constant type at " + index);
      }
  }

  public Type getType(ConstantPoolGen cpg) {
    switch(cpg.getConstantPool().getConstant(index).getTag()) {
    case org.apache.bcel.Constants.CONSTANT_String:  return Type.STRING;
    case org.apache.bcel.Constants.CONSTANT_Float:   return Type.FLOAT;
    case org.apache.bcel.Constants.CONSTANT_Integer: return Type.INT;
    default: // Never reached
      throw new RuntimeException("Unknown or invalid constant type at " + index);
    }
  }

  public Class[] getExceptions() {
    return org.apache.bcel.ExceptionConstants.EXCS_STRING_RESOLUTION;
  }

  /**
   * Call corresponding visitor method(s). The order is:
   * Call visitor methods of implemented interfaces first, then
   * call methods according to the class hierarchy in descending order,
   * i.e., the most specific visitXXX() call comes last.
   *
   * @param v Visitor object
   */
  public void accept(Visitor v) {
    v.visitStackProducer(this);
    v.visitPushInstruction(this);
    v.visitExceptionThrower(this);
    v.visitTypedInstruction(this);
    v.visitCPInstruction(this);
    v.visitLDC(this);
  }
}