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Java > Open Source Codes > com > sun > org > apache > bcel > internal > classfile > Constant


1 package com.sun.org.apache.bcel.internal.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
38  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 com.sun.org.apache.bcel.internal.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 1.1.1.1 2001/10/29 19:59:58 jvanzyl Exp $
66  * @author <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
67  */
68 public abstract class Constant implements Cloneable JavaDoc, Node {
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 JavaDoc 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 JavaDoc e) {}
112
113     return null;
114   }
115
116   public Object JavaDoc clone() throws CloneNotSupportedException JavaDoc {
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, ClassFormatError JavaDoc
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 ClassFormatError JavaDoc("Invalid byte tag in constant pool: " + b);
146     }
147   }
148 }
149
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