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Java > Open Source Codes > org > apache > bcel > classfile > Constant


1 /*
2  * Copyright 2000-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  *
16  */
17 package org.apache.bcel.classfile;
18
19 import java.io.DataInputStream JavaDoc;
20 import java.io.DataOutputStream JavaDoc;
21 import java.io.IOException JavaDoc;
22 import java.io.Serializable JavaDoc;
23 import org.apache.bcel.Constants;
24 import org.apache.bcel.util.BCELComparator;
25
26 /**
27  * Abstract superclass for classes to represent the different constant types
28  * in the constant pool of a class file. The classes keep closely to
29  * the JVM specification.
30  *
31  * @version $Id: Constant.java 386056 2006-03-15 11:31:56Z tcurdt $
32  * @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
33  */
34 public abstract class Constant implements Cloneable JavaDoc, Node, Serializable JavaDoc {
35
36     private static BCELComparator _cmp = new BCELComparator() {
37
38         public boolean equals( Object JavaDoc o1, Object JavaDoc o2 ) {
39             Constant THIS = (Constant) o1;
40             Constant THAT = (Constant) o2;
41             return THIS.toString().equals(THAT.toString());
42         }
43
44
45         public int hashCode( Object JavaDoc o ) {
46             Constant THIS = (Constant) o;
47             return THIS.toString().hashCode();
48         }
49     };
50     /* In fact this tag is redundant since we can distinguish different
51      * `Constant' objects by their type, i.e., via `instanceof'. In some
52      * places we will use the tag for switch()es anyway.
53      *
54      * First, we want match the specification as closely as possible. Second we
55      * need the tag as an index to select the corresponding class name from the
56      * `CONSTANT_NAMES' array.
57      */
58     protected byte tag;
59
60
61     Constant(byte tag) {
62         this.tag = tag;
63     }
64
65
66     /**
67      * Called by objects that are traversing the nodes of the tree implicitely
68      * defined by the contents of a Java class. I.e., the hierarchy of methods,
69      * fields, attributes, etc. spawns a tree of objects.
70      *
71      * @param v Visitor object
72      */
73     public abstract void accept( Visitor v );
74
75
76     public abstract void dump( DataOutputStream JavaDoc file ) throws IOException JavaDoc;
77
78
79     /**
80      * @return Tag of constant, i.e., its type. No setTag() method to avoid
81      * confusion.
82      */
83     public final byte getTag() {
84         return tag;
85     }
86
87
88     /**
89      * @return String representation.
90      */
91     public String JavaDoc toString() {
92         return Constants.CONSTANT_NAMES[tag] + "[" + tag + "]";
93     }
94
95
96     /**
97      * @return deep copy of this constant
98      */
99     public Constant copy() {
100         try {
101             return (Constant) super.clone();
102         } catch (CloneNotSupportedException JavaDoc e) {
103         }
104         return null;
105     }
106
107
108     public Object JavaDoc clone() throws CloneNotSupportedException JavaDoc {
109         return super.clone();
110     }
111
112
113     /**
114      * Read one constant from the given file, the type depends on a tag byte.
115      *
116      * @param file Input stream
117      * @return Constant object
118      */
119     static final Constant readConstant( DataInputStream JavaDoc file ) throws IOException JavaDoc,
120             ClassFormatException {
121         byte b = file.readByte(); // Read tag byte
122 switch (b) {
123             case Constants.CONSTANT_Class:
124                 return new ConstantClass(file);
125             case Constants.CONSTANT_Fieldref:
126                 return new ConstantFieldref(file);
127             case Constants.CONSTANT_Methodref:
128                 return new ConstantMethodref(file);
129             case Constants.CONSTANT_InterfaceMethodref:
130                 return new ConstantInterfaceMethodref(file);
131             case Constants.CONSTANT_String:
132                 return new ConstantString(file);
133             case Constants.CONSTANT_Integer:
134                 return new ConstantInteger(file);
135             case Constants.CONSTANT_Float:
136                 return new ConstantFloat(file);
137             case Constants.CONSTANT_Long:
138                 return new ConstantLong(file);
139             case Constants.CONSTANT_Double:
140                 return new ConstantDouble(file);
141             case Constants.CONSTANT_NameAndType:
142                 return new ConstantNameAndType(file);
143             case Constants.CONSTANT_Utf8:
144                 return new ConstantUtf8(file);
145             default:
146                 throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
147         }
148     }
149
150
151     /**
152      * @return Comparison strategy object
153      */
154     public static BCELComparator getComparator() {
155         return _cmp;
156     }
157
158
159     /**
160      * @param comparator Comparison strategy object
161      */
162     public static void setComparator( BCELComparator comparator ) {
163         _cmp = comparator;
164     }
165
166
167     /**
168      * Return value as defined by given BCELComparator strategy.
169      * By default two Constant objects are said to be equal when
170      * the result of toString() is equal.
171      *
172      * @see java.lang.Object#equals(java.lang.Object)
173      */
174     public boolean equals( Object JavaDoc obj ) {
175         return _cmp.equals(this, obj);
176     }
177
178
179     /**
180      * Return value as defined by given BCELComparator strategy.
181      * By default return the hashcode of the result of toString().
182      *
183      * @see java.lang.Object#hashCode()
184      */
185     public int hashCode() {
186         return _cmp.hashCode(this);
187     }
188 }
189
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