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ConstantValue.java

package de.fub.bytecode.classfile;

import  de.fub.bytecode.Constants;
import  java.io.*;

/**
 * This class is derived from <em>Attribute</em> and represents a constant 
 * value, i.e. a default value for initializing a class field.
 * This class is instantiated by the <em>Attribute.readAttribute()</em> method.
 *
 * @version $Id: ConstantValue.java,v 1.1.1.1 2002/01/24 03:44:00 pserver Exp $
 * @author  <A HREF="http://www.inf.fu-berlin.de/~dahm">M. Dahm</A>
 * @see     Attribute
 */
public final class ConstantValue extends Attribute {
  private int constantvalue_index;

  /**
   * @param name_index Name index in constant pool
   * @param length Content length in bytes
   * @param constantvalue_index Index in constant pool
   * @param constant_pool Array of constants
   */  
  public ConstantValue(int name_index, int length, 
               int constantvalue_index,
               ConstantPool constant_pool)
  {
    super(ATTR_CONSTANT_VALUE, name_index, length, constant_pool);
    this.constantvalue_index = constantvalue_index;
  }  
  /**
   * Construct object from file stream.
   * @param name_index Name index in constant pool
   * @param length Content length in bytes
   * @param file Input stream
   * @param constant_pool Array of constants
   * @throw IOException
   */
  ConstantValue(int name_index, int length, DataInputStream file,
        ConstantPool constant_pool) throws IOException
  {
    this(name_index, length, (int)file.readUnsignedShort(), constant_pool);
  }  
  /**
   * Initialize from another object. Note that both objects use the same
   * references (shallow copy). Use clone() for a physical copy.
   */
  public ConstantValue(ConstantValue c) {
    this(c.getNameIndex(), c.getLength(), c.getConstantValueIndex(),
     c.getConstantPool());
  }  
  /**
   * Called by objects that are traversing the nodes of the tree implicitely
   * defined by the contents of a Java class. I.e., the hierarchy of methods,
   * fields, attributes, etc. spawns a tree of objects.
   *
   * @param v Visitor object
   */
  public void accept(Visitor v) {
    v.visitConstantValue(this);
  }  
  /**
   * @return deep copy of this attribute
   */
  public Attribute copy(ConstantPool constant_pool) {
    ConstantValue c = (ConstantValue)clone();
    c.constant_pool = constant_pool;
    return c;
  }  
  /**
   * Dump constant value attribute to file stream on binary format.
   *
   * @param file Output file stream
   * @throw IOException
   */ 
  public final void dump(DataOutputStream file) throws IOException
  {
    super.dump(file);
    file.writeShort(constantvalue_index);
  }  
  /**
   * @return Index in constant pool of constant value.
   */  
  public final int getConstantValueIndex() { return constantvalue_index; }  
  /**
   * @param constantvalue_index.
   */
  public final void setConstantValueIndex(int constantvalue_index) {
    this.constantvalue_index = constantvalue_index;
  }  
  /**
   * @return String representation of constant value.
   */ 
  public final String toString() throws InternalError
  {
    Constant c = constant_pool.getConstant(constantvalue_index);
    
    String   buf;
    int    i;

    // Print constant to string depending on its type
    switch(c.getTag()) {
    case CONSTANT_Long:    buf = "" + ((ConstantLong)c).getBytes();    break;
    case CONSTANT_Float:   buf = "" + ((ConstantFloat)c).getBytes();   break;
    case CONSTANT_Double:  buf = "" + ((ConstantDouble)c).getBytes();  break;
    case CONSTANT_Integer: buf = "" + ((ConstantInteger)c).getBytes(); break;
    case CONSTANT_String:  
      i   = ((ConstantString)c).getStringIndex();
      c   = constant_pool.getConstant(i, CONSTANT_Utf8);
      buf = "\"" + ((ConstantUtf8)c).getBytes() + "\"";
      break;
    default: throw new InternalError("Type of ConstValue invalid: " + c);
    }

    return buf;
  }  
}

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