KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > com > vladium > jcd > cls > attribute > ConstantValueAttribute_info


1 /* Copyright (C) 2003 Vladimir Roubtsov. All rights reserved.
2  *
3  * This program and the accompanying materials are made available under
4  * the terms of the Common Public License v1.0 which accompanies this distribution,
5  * and is available at http://www.eclipse.org/legal/cpl-v10.html
6  *
7  * $Id: ConstantValueAttribute_info.java,v 1.1.1.1 2004/05/09 16:57:47 vlad_r Exp $
8  */
9 package com.vladium.jcd.cls.attribute;
10
11 import java.io.IOException JavaDoc;
12
13 import com.vladium.jcd.cls.ClassDef;
14 import com.vladium.jcd.cls.constant.CONSTANT_literal_info;
15 import com.vladium.jcd.lib.UDataInputStream;
16 import com.vladium.jcd.lib.UDataOutputStream;
17
18 // ----------------------------------------------------------------------------
19 /**
20  * The ConstantValue attribute is a fixed-length attribute used in the attributes
21  * table of the {@link com.vladium.jcd.cls.Field_info} structures. A ConstantValue
22  * attribute represents the value of a constant field that must be (explicitly or
23  * implicitly) static; that is, the ACC_STATIC bit in the flags item of the
24  * Field_info structure must be set. The field is not required to be final. There
25  * can be no more than one ConstantValue attribute in the attributes table of a
26  * given Field_info structure. The constant field represented by the Field_info
27  * structure is assigned the value referenced by its ConstantValue attribute as
28  * part of its initialization.<P>
29  *
30  * The ConstantValue attribute has the format
31  * <PRE>
32  * ConstantValue_attribute {
33  * u2 attribute_name_index;
34  * u4 attribute_length;
35  * u2 constantvalue_index;
36  * }
37  * </PRE>
38  *
39  * The value of the constantvalue_index item must be a valid index into the constant
40  * pool table. The constant pool entry at that index must give the constant value
41  * represented by this attribute.<P>
42  *
43  * The constant pool entry must be of a type appropriate to the field, as shown below:
44  *
45  * <TABLE>
46  * <TR><TH>Field Type</TH> <TH>Entry Type</TH></TR>
47  * <TR><TD>long</TD> <TD>CONSTANT_Long</TD></TR>
48  * <TR><TD>float</TD> <TD>CONSTANT_Float</TD></TR>
49  * <TR><TD>double</TD> <TD>CONSTANT_Double</TD></TR>
50  * <TR><TD>int, short, char, byte, boolean</TD> <TD>CONSTANT_Integer</TD></TR>
51  * <TR><TD>java.lang.String</TD> <TD>CONSTANT_String</TD></TR>
52  * </TABLE>
53  *
54  * @author (C) 2001, Vlad Roubtsov
55  */
56 public
57 final class ConstantValueAttribute_info extends Attribute_info
58 {
59     // public: ................................................................
60
61     
62     public int m_value_index;
63     
64     
65     public ConstantValueAttribute_info (final int attribute_name_index, final int value_index)
66     {
67         super (attribute_name_index, 2);
68         
69         m_value_index = value_index;
70     }
71     
72     public CONSTANT_literal_info getValue (final ClassDef cls)
73     {
74         return (CONSTANT_literal_info) cls.getConstants ().get (m_value_index);
75     }
76     
77     public long length ()
78     {
79         return 8;
80     }
81     
82     // Visitor:
83
84     public void accept (final IAttributeVisitor visitor, final Object JavaDoc ctx)
85     {
86         visitor.visit (this, ctx);
87     }
88     
89     public String JavaDoc toString ()
90     {
91         // TODO: return more data here
92 return "ConstantValueAttribute_info: [attribute_name_index = " + m_name_index + ", attribute_length = " + m_attribute_length + ']';
93     
94     }
95     
96     // Cloneable:
97
98     /**
99      * Performs a deep copy.
100      */
101     public Object JavaDoc clone ()
102     {
103         return super.clone ();
104     }
105     
106     // IClassFormatOutput:
107
108     public void writeInClassFormat (final UDataOutputStream out) throws IOException JavaDoc
109     {
110         super.writeInClassFormat (out);
111         
112         out.writeU2 (m_value_index);
113     }
114     
115     // protected: .............................................................
116
117     // package: ...............................................................
118
119
120     ConstantValueAttribute_info (final int attribute_name_index, final long attribute_length,
121                                  final UDataInputStream bytes)
122         throws IOException JavaDoc
123     {
124         super (attribute_name_index, attribute_length);
125         
126         m_value_index = bytes.readU2 ();
127         if (DEBUG) System.out.println ("\tconstantvalue_index: " + m_value_index);
128     }
129
130     // private: ...............................................................
131
132     
133     private static final boolean DEBUG = false;
134
135 } // end of class
136 // ----------------------------------------------------------------------------
137
Popular Tags