1   package org.apache.bcel.classfile;
2   
3   /* ====================================================================
4    * The Apache Software License, Version 1.1
5    *
6    * Copyright (c) 2001 The Apache Software Foundation.  All rights
7    * reserved.
8    *
9    * Redistribution and use in source and binary forms, with or without
10   * modification, are permitted provided that the following conditions
11   * are met:
12   *
13   * 1. Redistributions of source code must retain the above copyright
14   *    notice, this list of conditions and the following disclaimer.
15   *
16   * 2. Redistributions in binary form must reproduce the above copyright
17   *    notice, this list of conditions and the following disclaimer in
18   *    the documentation and/or other materials provided with the
19   *    distribution.
20   *
21   * 3. The end-user documentation included with the redistribution,
22   *    if any, must include the following acknowledgment:
23   *       "This product includes software developed by the
24   *        Apache Software Foundation (http://www.apache.org/)."
25   *    Alternately, this acknowledgment may appear in the software itself,
26   *    if and wherever such third-party acknowledgments normally appear.
27   *
28   * 4. The names "Apache" and "Apache Software Foundation" and
29   *    "Apache BCEL" must not be used to endorse or promote products
30   *    derived from this software without prior written permission. For
31   *    written permission, please contact apache@apache.org.
32   *
33   * 5. Products derived from this software may not be called "Apache",
34   *    "Apache BCEL", nor may "Apache" appear in their name, without
35   *    prior written permission of the Apache Software Foundation.
36   *
37   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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39   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48   * SUCH DAMAGE.
49   * ====================================================================
50   *
51   * This software consists of voluntary contributions made by many
52   * individuals on behalf of the Apache Software Foundation.  For more
53   * information on the Apache Software Foundation, please see
54   * <http://www.apache.org/>.
55   */
56  
57  import  org.apache.bcel.Constants;
58  import  java.io.*;
59  
60  /***
61   * Abstract superclass for classes to represent the different constant types
62   * in the constant pool of a class file. The classes keep closely to
63   * the JVM specification.
64   *
65   * @version $Id: Constant.java,v 1.3 2002/07/11 19:39:04 mdahm Exp $
66   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
67   */
68  public abstract class Constant implements Cloneable, Node, Serializable {
69    /* In fact this tag is redundant since we can distinguish different
70     * `Constant' objects by their type, i.e., via `instanceof'. In some
71     * places we will use the tag for switch()es anyway.
72     *
73     * First, we want match the specification as closely as possible. Second we
74     * need the tag as an index to select the corresponding class name from the 
75     * `CONSTANT_NAMES' array.
76     */
77    protected byte tag;
78  
79    Constant(byte tag) { this.tag = tag; }
80  
81    /***
82     * Called by objects that are traversing the nodes of the tree implicitely
83     * defined by the contents of a Java class. I.e., the hierarchy of methods,
84     * fields, attributes, etc. spawns a tree of objects.
85     *
86     * @param v Visitor object
87     */
88    public abstract void accept(Visitor v);    
89  
90    public abstract void dump(DataOutputStream file) throws IOException;    
91  
92    /***
93     * @return Tag of constant, i.e., its type. No setTag() method to avoid
94     * confusion.
95     */
96    public final byte getTag() { return tag; }
97  
98    /***
99     * @return String representation.
100    */  
101   public String toString() {
102     return Constants.CONSTANT_NAMES[tag] + "[" + tag + "]";
103   }    
104 
105   /***
106    * @return deep copy of this constant
107    */
108   public Constant copy() {
109     try {
110       return (Constant)super.clone();
111     } catch(CloneNotSupportedException e) {}
112 
113     return null;
114   }
115 
116   public Object clone() throws CloneNotSupportedException {
117     return super.clone();
118   }
119 
120   /***
121    * Read one constant from the given file, the type depends on a tag byte.
122    *
123    * @param file Input stream
124    * @return Constant object
125    */
126   static final Constant readConstant(DataInputStream file)
127     throws IOException, ClassFormatException
128   {
129     byte b = file.readByte(); // Read tag byte
130 
131     switch(b) {
132     case Constants.CONSTANT_Class:              return new ConstantClass(file);
133     case Constants.CONSTANT_Fieldref:           return new ConstantFieldref(file);
134     case Constants.CONSTANT_Methodref:          return new ConstantMethodref(file);
135     case Constants.CONSTANT_InterfaceMethodref: return new 
136 					ConstantInterfaceMethodref(file);
137     case Constants.CONSTANT_String:             return new ConstantString(file);
138     case Constants.CONSTANT_Integer:            return new ConstantInteger(file);
139     case Constants.CONSTANT_Float:              return new ConstantFloat(file);
140     case Constants.CONSTANT_Long:               return new ConstantLong(file);
141     case Constants.CONSTANT_Double:             return new ConstantDouble(file);
142     case Constants.CONSTANT_NameAndType:        return new ConstantNameAndType(file);
143     case Constants.CONSTANT_Utf8:               return new ConstantUtf8(file);
144     default:                          
145       throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
146     }
147   }    
148 }
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