constant.java

该开源工具主要用于class文件的操作

package org.apache.bcel.classfile;

/* ====================================================================
 * 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,
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 * 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  org.apache.bcel.Constants;
import  java.io.*;

/**
 * Abstract superclass for classes to represent the different constant types
 * in the constant pool of a class file. The classes keep closely to
 * the JVM specification.
 *
 * @version $Id: Constant.java,v 1.1.1.1 2001/10/29 19:59:58 jvanzyl Exp $
 * @author  <A HREF="mailto:[e-mail]">M. Dahm</A>
 */
public abstract class Constant implements Cloneable, Node {
  /* In fact this tag is redundant since we can distinguish different
   * `Constant' objects by their type, i.e., via `instanceof'. In some
   * places we will use the tag for switch()es anyway.
   *
   * First, we want match the specification as closely as possible. Second we
   * need the tag as an index to select the corresponding class name from the 
   * `CONSTANT_NAMES' array.
   */
  protected byte tag;

  Constant(byte tag) { this.tag = tag; }

  /**
   * Called by objects that are traversing the nodes of the tree implicitely
   * defined by the contents of a Java class. I.e., the hierarchy of methods,
   * fields, attributes, etc. spawns a tree of objects.
   *
   * @param v Visitor object
   */
  public abstract void accept(Visitor v);    

  public abstract void dump(DataOutputStream file) throws IOException;    

  /**
   * @return Tag of constant, i.e., its type. No setTag() method to avoid
   * confusion.
   */
  public final byte getTag() { return tag; }

  /**
   * @return String representation.
   */  
  public String toString() {
    return Constants.CONSTANT_NAMES[tag] + "[" + tag + "]";
  }    

  /**
   * @return deep copy of this constant
   */
  public Constant copy() {
    try {
      return (Constant)super.clone();
    } catch(CloneNotSupportedException e) {}

    return null;
  }

  public Object clone() throws CloneNotSupportedException {
    return super.clone();
  }

  /**
   * Read one constant from the given file, the type depends on a tag byte.
   *
   * @param file Input stream
   * @return Constant object
   */
  static final Constant readConstant(DataInputStream file)
    throws IOException, ClassFormatError
  {
    byte b = file.readByte(); // Read tag byte

    switch(b) {
    case Constants.CONSTANT_Class:              return new ConstantClass(file);
    case Constants.CONSTANT_Fieldref:           return new ConstantFieldref(file);
    case Constants.CONSTANT_Methodref:          return new ConstantMethodref(file);
    case Constants.CONSTANT_InterfaceMethodref: return new 
					ConstantInterfaceMethodref(file);
    case Constants.CONSTANT_String:             return new ConstantString(file);
    case Constants.CONSTANT_Integer:            return new ConstantInteger(file);
    case Constants.CONSTANT_Float:              return new ConstantFloat(file);
    case Constants.CONSTANT_Long:               return new ConstantLong(file);
    case Constants.CONSTANT_Double:             return new ConstantDouble(file);
    case Constants.CONSTANT_NameAndType:        return new ConstantNameAndType(file);
    case Constants.CONSTANT_Utf8:               return new ConstantUtf8(file);
    default:                          
      throw new ClassFormatError("Invalid byte tag in constant pool: " + b);
    }
  }    
}