Our customer (Ericsson Hewlett-Packard Telecommunications) claims that Bug ID 4294016 also exists in the Solaris version of JDK1.2.2_05 even if Bug ID 4294016 only is filed against the Windows_NT_95 version.

He is still seeing a JNI Global Reference to his
unreferenced objects when using JDK1.2.2_03 that has the fix for bug
4224888.

See the code example below.


import java.awt.*;
import java.awt.dnd.*;
import java.awt.dnd.peer.*;
import java.awt.event.*;
import java.awt.peer.*;
import javax.swing.*;

public class bugDropTargetLeak extends JFrame
{
  DropTarget _dt;

  public bugDropTargetLeak()
  {
    super("Test Window");

    _dt = new DropTarget(this, null);

    setSize(400, 400);
  }

  protected void processWindowEvent(WindowEvent we)
  {
    if (we.getID() == WindowEvent.WINDOW_CLOSING)
    {
      System.out.println("window closing...");
      if (_dt != null)
      {
        _dt.setComponent(null);

        // The following is to workaround the bug in removeDropTarget(), i.e.
        // we need to call it twice for it to invoke the native
        // removeNativeDropTarget(). getPeer() is a deprecated method, but
        // it's the only workaround I know of.
        ((DropTargetPeer)getPeer()).removeDropTarget(_dt);

        // Clear out the variable just so we have less clutter when analyzing
        // using HAT.
        _dt = null;
      }
      dispose();
    }

    super.processWindowEvent(we);
  }

  public static void main(String[] args)
  {
    JFrame f = new JFrame("Main Window");
    Container cp = f.getContentPane();
    JButton b = new JButton("Click me to launch a leaked window");

    f.getContentPane().add(b, "North");
    b.addActionListener(new ActionListener()
 {
      public void actionPerformed(ActionEvent ae)
      {
        (new bugDropTargetLeak()).setVisible(true);
      }
    });

    b = new JButton("gc()");
    f.getContentPane().add(b, "South");
    b.addActionListener(new ActionListener()
    {
      public void actionPerformed(ActionEvent ae)
      {
        System.out.print("Calling system.gc() and System.runFinalization(): ");
        System.gc();
        System.out.print(".");
        System.gc();
        System.out.print(".");
        System.runFinalization();
        System.out.print(".");
        System.gc();
        System.out.print(".");
        System.gc();
        System.out.print(".");
        System.runFinalization();
        System.out.print(".");
        System.gc();
        System.out.print(".");
        System.gc();
        System.out.println(" done");
      }
    });

    f.addWindowListener(new WindowAdapter()
    {
      public void windowClosing(WindowEvent we)
      {
        System.exit(0);
      }
    });

    f.pack();
    f.setVisible(true);
  }
}

jonas.edberg@sweden 2000-03-31