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1   /*
2    * reserved comment block
3    * DO NOT REMOVE OR ALTER!
4    */
5   package com.sun.org.apache.bcel.internal.classfile;
6   
7   /* ====================================================================
8    * The Apache Software License, Version 1.1
9    *
10   * Copyright (c) 2001 The Apache Software Foundation.  All rights
11   * reserved.
12   *
13   * Redistribution and use in source and binary forms, with or without
14   * modification, are permitted provided that the following conditions
15   * are met:
16   *
17   * 1. Redistributions of source code must retain the above copyright
18   *    notice, this list of conditions and the following disclaimer.
19   *
20   * 2. Redistributions in binary form must reproduce the above copyright
21   *    notice, this list of conditions and the following disclaimer in
22   *    the documentation and/or other materials provided with the
23   *    distribution.
24   *
25   * 3. The end-user documentation included with the redistribution,
26   *    if any, must include the following acknowledgment:
27   *       "This product includes software developed by the
28   *        Apache Software Foundation (http://www.apache.org/)."
29   *    Alternately, this acknowledgment may appear in the software itself,
30   *    if and wherever such third-party acknowledgments normally appear.
31   *
32   * 4. The names "Apache" and "Apache Software Foundation" and
33   *    "Apache BCEL" must not be used to endorse or promote products
34   *    derived from this software without prior written permission. For
35   *    written permission, please contact apache@apache.org.
36   *
37   * 5. Products derived from this software may not be called "Apache",
38   *    "Apache BCEL", nor may "Apache" appear in their name, without
39   *    prior written permission of the Apache Software Foundation.
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41   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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43   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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47   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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49   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
50   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
51   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
52   * SUCH DAMAGE.
53   * ====================================================================
54   *
55   * This software consists of voluntary contributions made by many
56   * individuals on behalf of the Apache Software Foundation.  For more
57   * information on the Apache Software Foundation, please see
58   * <http://www.apache.org/>.
59   */
60  
61  import  com.sun.org.apache.bcel.internal.Constants;
62  import  java.io.*;
63  
64  /**
65   * Abstract superclass for classes to represent the different constant types
66   * in the constant pool of a class file. The classes keep closely to
67   * the JVM specification.
68   *
69   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
70   */
71  public abstract class Constant implements Cloneable, Node, Serializable {
72    /* In fact this tag is redundant since we can distinguish different
73     * `Constant' objects by their type, i.e., via `instanceof'. In some
74     * places we will use the tag for switch()es anyway.
75     *
76     * First, we want match the specification as closely as possible. Second we
77     * need the tag as an index to select the corresponding class name from the
78     * `CONSTANT_NAMES' array.
79     */
80    protected byte tag;
81  
82    Constant(byte tag) { this.tag = tag; }
83  
84    /**
85     * Called by objects that are traversing the nodes of the tree implicitely
86     * defined by the contents of a Java class. I.e., the hierarchy of methods,
87     * fields, attributes, etc. spawns a tree of objects.
88     *
89     * @param v Visitor object
90     */
91    public abstract void accept(Visitor v);
92  
93    public abstract void dump(DataOutputStream file) throws IOException;
94  
95    /**
96     * @return Tag of constant, i.e., its type. No setTag() method to avoid
97     * confusion.
98     */
99    public final byte getTag() { return tag; }
100 
101   /**
102    * @return String representation.
103    */
104   public String toString() {
105     return Constants.CONSTANT_NAMES[tag] + "[" + tag + "]";
106   }
107 
108   /**
109    * @return deep copy of this constant
110    */
111   public Constant copy() {
112     try {
113       return (Constant)super.clone();
114     } catch(CloneNotSupportedException e) {}
115 
116     return null;
117   }
118 
119   public Object clone() throws CloneNotSupportedException {
120     return super.clone();
121   }
122 
123   /**
124    * Read one constant from the given file, the type depends on a tag byte.
125    *
126    * @param file Input stream
127    * @return Constant object
128    */
129   static final Constant readConstant(DataInputStream file)
130     throws IOException, ClassFormatException
131   {
132     byte b = file.readByte(); // Read tag byte
133 
134     switch(b) {
135     case Constants.CONSTANT_Class:              return new ConstantClass(file);
136     case Constants.CONSTANT_Fieldref:           return new ConstantFieldref(file);
137     case Constants.CONSTANT_Methodref:          return new ConstantMethodref(file);
138     case Constants.CONSTANT_InterfaceMethodref: return new
139                                         ConstantInterfaceMethodref(file);
140     case Constants.CONSTANT_String:             return new ConstantString(file);
141     case Constants.CONSTANT_Integer:            return new ConstantInteger(file);
142     case Constants.CONSTANT_Float:              return new ConstantFloat(file);
143     case Constants.CONSTANT_Long:               return new ConstantLong(file);
144     case Constants.CONSTANT_Double:             return new ConstantDouble(file);
145     case Constants.CONSTANT_NameAndType:        return new ConstantNameAndType(file);
146     case Constants.CONSTANT_Utf8:               return new ConstantUtf8(file);
147     default:
148       throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
149     }
150   }
151 }