/*
 * WeakRefVectorModel.java, (c) Raimond Reichert July 1999
 */
package mldemo;

import java.util.*;
import java.lang.ref.*;

/**
  * Implements <code>VectorModel</code> with weak references, ie, using
  * a <code>Vector</code> to hold <code>WeakReference</code>s which in turn
  * hold the references to the <code>VectorModel.Listener</code>s.
  *
  * <p>When ever a <code>VectorModel.Listener</code> event is fired,
  * "dead" listeners are removed when traversing the list of the listeners. 
  *
  * @author Raimond Reichert
  */
public class WeakRefVectorModel implements VectorModel {

  private Vector vector;
  private Vector listeners;

  public WeakRefVectorModel() {
    vector    = new Vector();
    listeners = new Vector();
  } // WeakRefVectorModel //

  public void addElement (Object object) {
    vector.addElement (object);
    fireElementAdded (object);
  } // addElement //

  public void removeElement (Object object) {
    vector.removeElement (object);
    fireElementRemoved (object);
  } // removeElement //

  public Object elementAt (int index) {
    return vector.elementAt (index);
  } // elementAt //

  public int size() {
    return vector.size();
  } // size //

  public void addListener (VectorModel.Listener l) {
    WeakReference wr = new WeakReference (l);
    listeners.addElement (wr);
  } // addListener //

  /**
    * When looking up <code>l</code>, weak references which have been cleared
    * (ie, they reference only <code>null</code> anymore) are thrown out
    * of the <code>listeners</code> vector.
    */
  public void removeListener (VectorModel.Listener l) {
    int size = listeners.size();
    int i = 0;
    while (i < size) {
      WeakReference wr = (WeakReference)listeners.elementAt(i);
      VectorModel.Listener vml = (VectorModel.Listener)wr.get();
      if (vml == null) {
        listeners.removeElement (wr);
        size--;
      }
      else {
        if (vml == l)
          listeners.removeElement (wr);
        i++;
      }
    }
  } // removeListener //

  /**
    * When firing the event, weak references which have been cleared
    * (ie, they reference only <code>null</code> anymore) are thrown out
    * of the <code>listeners</code> vector.
    */
  protected void fireElementAdded (Object object) {
    VectorModel.Event e = null;
    int size = listeners.size();
    int i = 0;

    while (i < size) {
      WeakReference wr = (WeakReference)listeners.elementAt(i);
      VectorModel.Listener vml = (VectorModel.Listener)wr.get();
      if (vml == null) {
        listeners.removeElement (wr);
        size--;
        System.out.println (
          "WeakRefVectorModel.fireElementAdded: found dead reference"
        );
      }
      else {
        if (e == null) // lazily create event
          e = new VectorModel.Event (this, object);
        vml.elementAdded (e);
        i++;
      }
    }
  } // fireElementAdded //

  protected void fireElementRemoved (Object object) {
    VectorModel.Event e = null;
    int size = listeners.size();
    int i = 0;

    while (i < size) {
      WeakReference wr = (WeakReference)listeners.elementAt(i);
      VectorModel.Listener vml = (VectorModel.Listener)wr.get();
      if (vml == null) {
        listeners.removeElement (wr);
        size--;
        System.out.println (
          "WeakRefVectorModel.fireElementRemoved: found dead reference"
        );
      }
      else {
        if (e == null) // lazily create event
          e = new VectorModel.Event (this, object);
        vml.elementRemoved (e);
        i++;
      }
    }
  } // fireElementRemoved //

} // WeakRefVectorModel //