View Javadoc

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;
20  import java.io.DataOutputStream;
21  import java.io.IOException;
22  import org.apache.bcel.Constants;
23  
24  /*** 
25   * This class is derived from the abstract 
26   * <A HREF="org.apache.bcel.classfile.Constant.html">Constant</A> class 
27   * and represents a reference to a String object.
28   *
29   * @version $Id: ConstantString.java 386056 2006-03-15 11:31:56Z tcurdt $
30   * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
31   * @see     Constant
32   */
33  public final class ConstantString extends Constant implements ConstantObject {
34  
35      private int string_index; // Identical to ConstantClass except for this name
36  
37  
38      /***
39       * Initialize from another object.
40       */
41      public ConstantString(ConstantString c) {
42          this(c.getStringIndex());
43      }
44  
45  
46      /*** 
47       * Initialize instance from file data.
48       *
49       * @param file Input stream
50       * @throws IOException
51       */
52      ConstantString(DataInputStream file) throws IOException {
53          this(file.readUnsignedShort());
54      }
55  
56  
57      /***
58       * @param string_index Index of Constant_Utf8 in constant pool
59       */
60      public ConstantString(int string_index) {
61          super(Constants.CONSTANT_String);
62          this.string_index = string_index;
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 void accept( Visitor v ) {
74          v.visitConstantString(this);
75      }
76  
77  
78      /***
79       * Dump constant field reference to file stream in binary format.
80       *
81       * @param file Output file stream
82       * @throws IOException
83       */
84      public final void dump( DataOutputStream file ) throws IOException {
85          file.writeByte(tag);
86          file.writeShort(string_index);
87      }
88  
89  
90      /***
91       * @return Index in constant pool of the string (ConstantUtf8).
92       */
93      public final int getStringIndex() {
94          return string_index;
95      }
96  
97  
98      /***
99       * @param string_index the index into the constant of the string value
100      */
101     public final void setStringIndex( int string_index ) {
102         this.string_index = string_index;
103     }
104 
105 
106     /***
107      * @return String representation.
108      */
109     public final String toString() {
110         return super.toString() + "(string_index = " + string_index + ")";
111     }
112 
113 
114     /*** @return String object
115      */
116     public Object getConstantValue( ConstantPool cp ) {
117         Constant c = cp.getConstant(string_index, Constants.CONSTANT_Utf8);
118         return ((ConstantUtf8) c).getBytes();
119     }
120 
121 
122     /*** @return dereferenced string
123      */
124     public String getBytes( ConstantPool cp ) {
125         return (String) getConstantValue(cp);
126     }
127 }