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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   *  Unless required by applicable law or agreed to in writing, software
12   *  distributed under the License is distributed on an "AS IS" BASIS,
13   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   *  See the License for the specific language governing permissions and
15   *  limitations under the License.
16   *
17   */
18  package org.apache.bcel.classfile;
19  
20  import java.io.DataInput;
21  import java.io.DataOutputStream;
22  import java.io.IOException;
23  
24  import org.apache.bcel.Const;
25  import org.apache.bcel.util.BCELComparator;
26  
27  /**
28   * Abstract superclass for classes to represent the different constant types
29   * in the constant pool of a class file. The classes keep closely to
30   * the JVM specification.
31   *
32   * @version $Id: Constant.html 1021978 2017-12-09 17:38:21Z ggregory $
33   */
34  public abstract class Constant implements Cloneable, Node {
35  
36      private static BCELComparator bcelComparator = new BCELComparator() {
37  
38          @Override
39          public boolean equals( final Object o1, final Object o2 ) {
40              final Constant THIS = (Constant) o1;
41              final Constant THAT = (Constant) o2;
42              return THIS.toString().equals(THAT.toString());
43          }
44  
45  
46          @Override
47          public int hashCode( final Object o ) {
48              final Constant THIS = (Constant) o;
49              return THIS.toString().hashCode();
50          }
51      };
52      /* In fact this tag is redundant since we can distinguish different
53       * `Constant' objects by their type, i.e., via `instanceof'. In some
54       * places we will use the tag for switch()es anyway.
55       *
56       * First, we want match the specification as closely as possible. Second we
57       * need the tag as an index to select the corresponding class name from the
58       * `CONSTANT_NAMES' array.
59       */
60      /**
61       * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
62       */
63      @java.lang.Deprecated
64      protected byte tag; // TODO should be private & final
65  
66  
67      Constant(final byte tag) {
68          this.tag = tag;
69      }
70  
71  
72      /**
73       * Called by objects that are traversing the nodes of the tree implicitely
74       * defined by the contents of a Java class. I.e., the hierarchy of methods,
75       * fields, attributes, etc. spawns a tree of objects.
76       *
77       * @param v Visitor object
78       */
79      @Override
80      public abstract void accept( Visitor v );
81  
82  
83      public abstract void dump( DataOutputStream file ) throws IOException;
84  
85  
86      /**
87       * @return Tag of constant, i.e., its type. No setTag() method to avoid
88       * confusion.
89       */
90      public final byte getTag() {
91          return tag;
92      }
93  
94  
95      /**
96       * @return String representation.
97       */
98      @Override
99      public String toString() {
100         return Const.getConstantName(tag) + "[" + tag + "]";
101     }
102 
103 
104     /**
105      * @return deep copy of this constant
106      */
107     public Constant copy() {
108         try {
109             return (Constant) super.clone();
110         } catch (final CloneNotSupportedException e) {
111             // TODO should this throw?
112         }
113         return null;
114     }
115 
116 
117     @Override
118     public Object clone() {
119         try {
120             return super.clone();
121         } catch (final CloneNotSupportedException e) {
122             throw new Error("Clone Not Supported"); // never happens
123         }
124     }
125 
126 
127     /**
128      * Read one constant from the given input, the type depends on a tag byte.
129      *
130      * @param input Input stream
131      * @return Constant object
132      * @since 6.0 made public
133      */
134     public static Constant readConstant( final DataInput input ) throws IOException,
135             ClassFormatException {
136         final byte b = input.readByte(); // Read tag byte
137         switch (b) {
138             case Const.CONSTANT_Class:
139                 return new ConstantClass(input);
140             case Const.CONSTANT_Fieldref:
141                 return new ConstantFieldref(input);
142             case Const.CONSTANT_Methodref:
143                 return new ConstantMethodref(input);
144             case Const.CONSTANT_InterfaceMethodref:
145                 return new ConstantInterfaceMethodref(input);
146             case Const.CONSTANT_String:
147                 return new ConstantString(input);
148             case Const.CONSTANT_Integer:
149                 return new ConstantInteger(input);
150             case Const.CONSTANT_Float:
151                 return new ConstantFloat(input);
152             case Const.CONSTANT_Long:
153                 return new ConstantLong(input);
154             case Const.CONSTANT_Double:
155                 return new ConstantDouble(input);
156             case Const.CONSTANT_NameAndType:
157                 return new ConstantNameAndType(input);
158             case Const.CONSTANT_Utf8:
159                 return ConstantUtf8.getInstance(input);
160             case Const.CONSTANT_MethodHandle:
161                 return new ConstantMethodHandle(input);
162             case Const.CONSTANT_MethodType:
163                 return new ConstantMethodType(input);
164             case Const.CONSTANT_InvokeDynamic:
165                 return new ConstantInvokeDynamic(input);
166             case Const.CONSTANT_Module:
167                 return new ConstantModule(input);
168             case Const.CONSTANT_Package:
169                 return new ConstantPackage(input);
170             default:
171                 throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
172         }
173     }
174 
175 
176     /**
177      * @return Comparison strategy object
178      */
179     public static BCELComparator getComparator() {
180         return bcelComparator;
181     }
182 
183 
184     /**
185      * @param comparator Comparison strategy object
186      */
187     public static void setComparator( final BCELComparator comparator ) {
188         bcelComparator = comparator;
189     }
190 
191 
192     /**
193      * Return value as defined by given BCELComparator strategy.
194      * By default two Constant objects are said to be equal when
195      * the result of toString() is equal.
196      *
197      * @see java.lang.Object#equals(java.lang.Object)
198      */
199     @Override
200     public boolean equals( final Object obj ) {
201         return bcelComparator.equals(this, obj);
202     }
203 
204 
205     /**
206      * Return value as defined by given BCELComparator strategy.
207      * By default return the hashcode of the result of toString().
208      *
209      * @see java.lang.Object#hashCode()
210      */
211     @Override
212     public int hashCode() {
213         return bcelComparator.hashCode(this);
214     }
215 }