fieldgen.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.generic;

import de.fub.bytecode.Constants;
import de.fub.bytecode.classfile.*;
import java.util.Vector;
import java.util.Enumeration;

/** 
 * Template class for building up a field.  The only extraordinary thing
 * one can do is to add a constant value attribute to a field (which must of
 * course be compatible with to the declared type).
 *
 * @version $Id: FieldGen.java,v 1.13 2001/10/11 11:59:27 dahm Exp $
 * @author  <A HREF="http://www.berlin.de/~markus.dahm/">M. Dahm</A>
 * @see Field
 */
public class FieldGen extends FieldGenOrMethodGen {
  private Object value = null;

  /**
   * Declare a field. If it is static (isStatic() == true) and has a
   * basic type like int or String it may have an initial value
   * associated with it as defined by setInitValue().
   *
   * @param access_flags access qualifiers
   * @param type  field type
   * @param name field name
   * @param cp constant pool
   */
  public FieldGen(int access_flags, Type type, String name, ConstantPoolGen cp) {
    setAccessFlags(access_flags);
    setType(type);
    setName(name);
    setConstantPool(cp);
  }

  /**
   * Instantiate from existing field.
   *
   * @param field Field object
   * @param cp constant pool (must contain the same entries as the field's constant pool)
   */
  public FieldGen(Field field, ConstantPoolGen cp) {
    this(field.getAccessFlags(), Type.getType(field.getSignature()), field.getName(), cp);

    Attribute[] attrs = field.getAttributes();

    for(int i=0; i < attrs.length; i++) {
      if(attrs[i] instanceof ConstantValue)
	setValue(((ConstantValue)attrs[i]).getConstantValueIndex());
      else
	addAttribute(attrs[i]);
    }
  }

  private void setValue(int index) {
    ConstantPool cp  = this.cp.getConstantPool();
    Constant     c   = cp.getConstant(index);
    value = ((ConstantObject)c).getConstantValue(cp);
  }

  /**
   * Set (optional) initial value of field, otherwise it will be set to null/0/false
   * by the JVM automatically.
   */
  public void setInitValue(String str) {
    checkType(new ObjectType("java.lang.String"));

    if(str != null)
      value = str;
  }

  public void setInitValue(long l) {
    checkType(Type.LONG);

    if(l != 0L)
      value = new Long(l);
  }

  public void setInitValue(int i) {
    checkType(Type.INT);

    if(i != 0)
      value = new Integer(i);
  }

  public void setInitValue(short s) {
    checkType(Type.SHORT);

    if(s != 0)
      value = new Integer(s);
  }

  public void setInitValue(char c) {
    checkType(Type.CHAR);

    if(c != 0)
      value = new Integer(c);
  }

  public void setInitValue(byte b) {
    checkType(Type.BYTE);

    if(b != 0)
      value = new Integer(b);
  }

  public void setInitValue(boolean b) {
    checkType(Type.BOOLEAN);

    if(b)
      value = new Integer(1);
  }

  public void setInitValue(float f) {
    checkType(Type.FLOAT);

    if(f != 0.0)
      value = new Float(f);
  }

  public void setInitValue(double d) {
    checkType(Type.DOUBLE);

    if(d != 0.0)
      value = new Double(d);
  }

  /** Remove any initial value.
   */
  public void cancelInitValue() {
    value = null;
  }

  private void checkType(Type atype) {
    if(type == null)
      throw new ClassGenException("You haven't defined the type of the field yet");
    
    if(!isFinal())
      throw new ClassGenException("Only final fields may have an initial value!");

    if(!type.equals(atype))
      throw new ClassGenException("Types are not compatible: " + type + " vs. " + atype);
  }

  /**
   * Get field object after having set up all necessary values.
   */
  public Field getField() {
    String      signature       = getSignature();
    int         name_index      = cp.addUtf8(name);
    int         signature_index = cp.addUtf8(signature);

    if(value != null) {
      checkType(type);
      int index = addConstant();
      addAttribute(new ConstantValue(cp.addUtf8("ConstantValue"),
				     2, index, cp.getConstantPool()));
    }

    return new Field(access_flags, name_index, signature_index, getAttributes(),
		     cp.getConstantPool());
  }

  private int addConstant() {
    switch(type.getType()) {
    case Constants.T_INT: case Constants.T_CHAR: case Constants.T_BYTE:
    case Constants.T_BOOLEAN: case Constants.T_SHORT:
      return cp.addInteger(((Integer)value).intValue());
      
    case Constants.T_FLOAT:
      return cp.addFloat(((Float)value).floatValue());

    case Constants.T_DOUBLE:
      return cp.addDouble(((Double)value).doubleValue());

    case Constants.T_LONG:
      return cp.addLong(((Long)value).longValue());

    case Constants.T_REFERENCE:
      return cp.addString(((String)value));

    default:
      throw new RuntimeException("Oops: Unhandled : " + type.getType());
    }
  }

  public String  getSignature()  { return type.getSignature(); }

  private Vector observers;

  /** Add observer for this object.
   */
  public void addObserver(FieldObserver o) {
    if(observers == null)
      observers = new Vector();

    observers.addElement(o);
  }

  /** Remove observer for this object.
   */
  public void removeObserver(FieldObserver o) {
    if(observers != null)
      observers.removeElement(o);
  }

  /** Call notify() method on all observers. This method is not called
   * automatically whenever the state has changed, but has to be
   * called by the user after he has finished editing the object.
   */
  public void update() {
    if(observers != null)
      for(Enumeration e = observers.elements(); e.hasMoreElements(); )
	((FieldObserver)e.nextElement()).notify(this);
  }

  public String getInitValue() {
    if(value != null) {
      return value.toString();
    } else
      return null;
  }

  /**
   * Return string representation close to declaration format,
   * `public static final short MAX = 100', e.g..
   *
   * @return String representation of field
   */
  public final String toString() {
    String name, signature, access; // Short cuts to constant pool

    access    = Utility.accessToString(access_flags);
    access    = access.equals("")? "" : (access + " ");
    signature = type.toString();
    name      = getName();

    StringBuffer buf = new StringBuffer(access + signature + " " + name);
    String value = getInitValue();

    if(value != null)
      buf.append(" = " + value);

    return buf.toString();
  }

  /** @return deep copy of this field
   */
  public FieldGen copy(ConstantPoolGen cp) {
    FieldGen fg = (FieldGen)clone();

    fg.setConstantPool(cp);
    return fg;
  }
}