constantvalue.java

代码是一个分类器的实现,其中使用了部分weka的源代码。可以将项目导入eclipse运行

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 1.3 2001/05/09 09:26:57 dahm Exp $
 * @author  <A HREF="http://www.berlin.de/~markus.dahm/">M. Dahm</A>
 * @see     Attribute
 */
public final class ConstantValue extends Attribute {
  private int constantvalue_index;

  /**
   * 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());
  }

  /**
   * 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);
  }    

  /**
   * @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(Constants.ATTR_CONSTANT_VALUE, name_index, length, constant_pool);
    this.constantvalue_index = constantvalue_index;
  }    

  /**
   * 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);
  }    
  /**
   * 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 Constants.CONSTANT_Long:    buf = "" + ((ConstantLong)c).getBytes();    break;
    case Constants.CONSTANT_Float:   buf = "" + ((ConstantFloat)c).getBytes();   break;
    case Constants.CONSTANT_Double:  buf = "" + ((ConstantDouble)c).getBytes();  break;
    case Constants.CONSTANT_Integer: buf = "" + ((ConstantInteger)c).getBytes(); break;
    case Constants.CONSTANT_String:  
      i   = ((ConstantString)c).getStringIndex();
      c   = constant_pool.getConstant(i, Constants.CONSTANT_Utf8);
      buf = "\"" + convertString(((ConstantUtf8)c).getBytes()) + "\"";
      break;
    default: throw new InternalError("Type of ConstValue invalid: " + c);
    }

    return buf;
  }

  /**
   * Escape all occurences of newline chars '\n', quotes \", etc.
   */
  private static final String convertString(String label) {
    char[]       ch  = label.toCharArray();
    StringBuffer buf = new StringBuffer();

    for(int i=0; i < ch.length; i++) {
      switch(ch[i]) {
      case '\n':
	buf.append("\\n"); break;
      case '\r':
	buf.append("\\r"); break;
      case '\"':
	buf.append("\\\""); break;
      case '\'':
	buf.append("\\'"); break;
      case '\\':
	buf.append("\\\\"); break;
      default:
	buf.append(ch[i]); break;
      }
    }

    return buf.toString();
  }

  /**
   * @return deep copy of this attribute
   */
  public Attribute copy(ConstantPool constant_pool) {
    ConstantValue c = (ConstantValue)clone();
    c.constant_pool = constant_pool;
    return c;
  }
}