---

Attribute.java

package de.fub.bytecode.classfile;

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

/**
 * Abstract super class for <em>Attribute</em> objects. Currently the
 * <em>ConstantValue</em>, <em>SourceFile</em>, <em>Code</em>,
 * <em>Exceptiontable</em>, <em>LineNumberTable</em>, 
 * <em>LocalVariableTable</em>, <em>InnerClasses</em> and
 * <em>Synthetic</em> attributes are supported. The
 * <em>Unknown</em> attribute stands for non-standard-attributes.
 *
 * @version $Id: Attribute.java,v 1.1.1.1 2002/01/24 03:41:37 pserver Exp $
 * @author  <A HREF="http://www.inf.fu-berlin.de/~dahm">M. Dahm</A>
 * @see     ConstantValue
 * @see     SourceFile
 * @see     Code
 * @see     Unknown
 * @see     ExceptionTable
 * @see     LineNumberTable
 * @see     LocalVariableTable 
 * @see     InnerClasses
 * @see     Synthetic
 * @see     Deprecated
*/
public abstract class Attribute implements Cloneable
{
  protected int          name_index; // Points to attribute name in constant pool
  protected int          length;     // Content length of attribute field
  protected byte         tag;        // Tag to distiguish subclasses
  protected ConstantPool constant_pool;

  Attribute(byte tag, int name_index, int length, ConstantPool constant_pool) {
    this.tag           = tag;
    this.name_index    = name_index;
    this.length        = length;
    this.constant_pool = constant_pool;
  }  
  /**
   * 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 abstract void accept(Visitor v);  
  /**
   * Use copy() if you want to have a deep copy(), i.e., with all references
   * copied correctly.
   *
   * @return shallow copy of this attribute
   */
  public Object clone() {
    Object o = null;

    try {
      o = super.clone();
    } catch(CloneNotSupportedException e) {
      e.printStackTrace(); // Never occurs
    }

    return o;
  }  
  /**
   * @return deep copy of this attribute
   */
  public abstract Attribute copy(ConstantPool constant_pool);  
  /**
   * Dump attribute to file stream in binary format.
   *
   * @param file Output file stream
   * @throw IOException
   */
  public void dump(DataOutputStream file) throws IOException
  {
    file.writeShort(name_index);
    file.writeInt(length);
  }  
  /**
   * @return Constant pool used by this object.
   * @see ConstantPool
   */   
  public final ConstantPool getConstantPool() { return constant_pool; }  
  /**
   * @return Length of attribute field in bytes.
   */  
  public final int   getLength()    { return length; }  
  /**
   * @return Name index in constant pool of attribute name.
   */  
  public final int getNameIndex() { return name_index; }  
  /**
   * @return Tag of attribute, i.e., its type. Value may not be altered, thus
   * there is no setTag() method.
   */
  public final byte  getTag()       { return tag; }  
  /* Class method reads one attribute from the input data stream.
   * This method must not be accessible from the outside.
   * It is called by the <A HREF="DE.fub.inf.JavaClass.Field.html">
   * Field</A> and <A HREF="DE.fub.inf.JavaClass.Method.html">
   * Method</A> constructor methods.
   *
   * @see    Field
   * @see    Method
   * @param  file Input stream
   * @param  constant_pool Array of constants
   * @return Attribute
   * @throw  IOException
   * @throw  ClassFormatError
   * @throw  InternalError
   */
  static final Attribute readAttribute(DataInputStream file,
                       ConstantPool constant_pool)
    throws IOException, ClassFormatError, InternalError
  {
    ConstantUtf8 c;
    String       name;
    int          name_index;
    int          length;
    byte         tag = Constants.ATTR_UNKNOWN; // Unknown attribute

    // Get class name from constant pool via `name_index' indirection
    name_index = (int)(file.readUnsignedShort());
    c          = (ConstantUtf8)constant_pool.getConstant(name_index, 
                             Constants.CONSTANT_Utf8);
    name       = c.getBytes();

    // Length of data in bytes
    length     = file.readInt();

    // Compare strings to find known attribute
    for(byte i=0; i < Constants.KNOWN_ATTRIBUTES; i++) {
      if(name.equals(Constants.ATTRIBUTE_NAMES[i])) {
    tag = i; // found!
    break;
      }
    }

    // Call proper constructor, depending on `tag'
    switch(tag) {
    case Constants.ATTR_UNKNOWN:
      return new Unknown(name_index, length, file, constant_pool);

    case Constants.ATTR_CONSTANT_VALUE:
      return new ConstantValue(name_index, length, file, constant_pool);

    case Constants.ATTR_SOURCE_FILE:
      return new SourceFile(name_index, length, file, constant_pool);
      
    case Constants.ATTR_CODE:
      return new Code(name_index, length, file, constant_pool);
      
    case Constants.ATTR_EXCEPTIONS:
      return new ExceptionTable(name_index, length, file, constant_pool);
      
    case Constants.ATTR_LINE_NUMBER_TABLE:
      return new LineNumberTable(name_index, length, file, constant_pool);
      
    case Constants.ATTR_LOCAL_VARIABLE_TABLE:
      return new LocalVariableTable(name_index, length, file, constant_pool);

    case Constants.ATTR_INNER_CLASSES:
      return new InnerClasses(name_index, length, file, constant_pool);

    case Constants.ATTR_SYNTHETIC:
      return new Synthetic(name_index, length, file, constant_pool);

    case Constants.ATTR_DEPRECATED:
      return new Deprecated(name_index, length, file, constant_pool);

    case Constants.ATTR_PMG:
      return new PMGClass(name_index, length, file, constant_pool);

    case Constants.ATTR_SIGNATURE:
      return new Signature(name_index, length, file, constant_pool);

    default: // Never reached
      throw new InternalError("Ooops! default case reached.");
    }
  }  
  /**
   * @param constant_pool Constant pool to be used for this object.
   * @see ConstantPool
   */   
  public final void setConstantPool(ConstantPool constant_pool) {
    this.constant_pool = constant_pool;
  }  
  /**
   * @param Attribute length in bytes.
   */
  public final void setLength(int length) {
    this.length = length;
  }  
  /**
   * @param name_index of attribute.
   */
  public final void setNameIndex(int name_index) {
    this.name_index = name_index;
  }  
  /**
   * @return attribute name.
   */ 
  public String toString() {
    return Constants.ATTRIBUTE_NAMES[tag];
  }  
}

---