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      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;
     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 ctx)
     85     {
     86         visitor.visit (this, ctx);
     87     }
     88 
     89     public String 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 clone ()
    102     {
    103         return super.clone ();
    104     }
    105 
    106     // IClassFormatOutput:
    107 
    108     public void writeInClassFormat (final UDataOutputStream out) throws IOException
    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
    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