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

public class Test
{

  //Run this as "java -verbosegc -Xmx1m -Xms1m Test"
  //However the 1.2 JVM crashes the main thread when I flush the memory
  //and puts the GC thread into a loop if you use -verbosegc
  //So use only the 1.3 JVM.
  public static void main(String[] args)
  {
    test();
  }


  static Object DUMMY_OBJ = new Object();

  public static void test()
  {
    String key = new String("hi");
    String value = "xyz";
    String equalKey = new String("hi");

    //construction
    WeakHashMap aWeakHashMap = new WeakHashMap();
    HashMap aHashMap = new HashMap();
    ReferenceQueue Queue = new ReferenceQueue();

    //update
    aWeakHashMap.put(key, value);
    MyWeakReference RefKey = new MyWeakReference(key, Queue);
    aHashMap.put(RefKey, value);
    System.out.println(RefKey.get() == key);

    //access
    System.out.println(aWeakHashMap.get(equalKey) == value);
    System.out.println(aWeakHashMap.get(key) == value);
    MyWeakReference RefKey2 = new MyWeakReference(equalKey, Queue);
    System.out.println(aHashMap.get(RefKey2) == value);
    System.out.println(aHashMap.get(RefKey) == value);

    //force gc of the weakly held key
    key = null;
    flushMemory();
    System.out.println(RefKey.get() == null);

    //Access again
    System.out.println(aWeakHashMap.get(equalKey) == null);
    MyWeakReference RefKey3 = new MyWeakReference(equalKey, Queue);
    System.out.println(aHashMap.get(RefKey3) == null);

    //Process ref objs
    aWeakHashMap.put(DUMMY_OBJ, DUMMY_OBJ);
    MyWeakReference aRef;
    while ((aRef = (MyWeakReference) Queue.poll()) != null)
    {
      System.out.println(aRef == RefKey);
      aHashMap.remove(aRef);
    }

  }


  public static void flushMemory()
  {
    Vector v = new Vector();
    int count = 0;
    int size = 1048576;
    while(size > 1)
    {
      try
      {
        for (; true ; count++)
        {
          v.addElement( new byte[size] );
        }
      }
      catch(OutOfMemoryError bounded){size = size/2;}
    }
    v = null; //release for GC
    v = new Vector();
  }
}


class MyWeakReference extends WeakReference
{
  //We need to store the hash code separately since the referent
  //could be removed by the GC.
  int hash;

  public MyWeakReference(Object o, ReferenceQueue q)
  {
    super(o,q);
    hash = o.hashCode();
  }

  public int hashCode()
  {
    return hash;
  }

  public boolean equals(Object o)
  {
    if (this == o) return true;
    if (!(o instanceof MyWeakReference)) return false;
    Object t = this.get();
    Object u = ((MyWeakReference)o).get();
    if ((t == null) || (u == null)) return false;
    if (t == u) return true;
    return t.equals(u);
  }
}