Name: rlT66838 Date: 08/25/99


I'm seeing an intermittent null pointer exception when I run a
program which uses the SwingWorker class from The Swing Connection
web site:

  http://java.sun.com/products/jfc/tsc/archive/tech_topics_arch/swing_worker/SwingWorker.java

It doesn't matter which compiler I've used: I tried javac from
JDK 1.2.2 and JDK 1.3, and jikes. The problem only occurs when I
use the JDK 1.3 java with HotSpot. It doesn't happen with the
JDK 1.2.2 java, nor JDK 1.3 java with the -classic flag, nor JDK
1.1.8.

It only happens *sometimes* with JDK 1.3. Here's a transcript of
some attempts showing three failures and one success:

tiffany> /opt4/jdk1.3/bin/java WorkerBug
java.lang.NullPointerException
        at WorkerBug.access$000(WorkerBug.java:5)
        at WorkerBug$MyWorker.construct(WorkerBug.java:34)
        at SwingWorker$2.run(SwingWorker.java:101)
        at java.lang.Thread.run(Thread.java:479)
tiffany> /opt4/jdk1.3/bin/java WorkerBug
java.lang.NullPointerException
        at WorkerBug.access$000(WorkerBug.java:5)
        at WorkerBug$MyWorker.construct(WorkerBug.java:34)
        at SwingWorker$2.run(SwingWorker.java:101)
        at java.lang.Thread.run(Thread.java:479)
tiffany> /opt4/jdk1.3/bin/java WorkerBug
Hello world
tiffany> /opt4/jdk1.3/bin/java WorkerBug
java.lang.NullPointerException
        at WorkerBug.access$000(WorkerBug.java:5)
        at WorkerBug$MyWorker.construct(WorkerBug.java:34)
        at SwingWorker$2.run(SwingWorker.java:101)
        at java.lang.Thread.run(Thread.java:479)
tiffany>

And here's the program:

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

public class WorkerBug extends JFrame {
    private String query ;

    public WorkerBug() {
        JPanel panel = new JPanel() ;

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

        getContentPane().add(panel) ;
        setBounds(200, 200, 640, 480);
        setVisible(true);
    }

    public void doSomething() {
        query = "Hello world" ;
        new MyWorker() ;
    }

    public static void main(String s[]) {
        WorkerBug wb = new WorkerBug() ;
        wb.doSomething() ;
    }

    private class MyWorker extends SwingWorker {
        public Object construct() {
            System.out.println(query) ;
            return query ;
        }
    }
}

And the JVM version:

tiffany> /opt4/jdk1.3/bin/java -version
java version "1.3beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3beta-O)
Java(TM) HotSpot Client VM (build 1.3beta-O-release, 1.3beta-O-release, interpreted mode)
tiffany> /opt4/jdk1.3/bin/java -fullversion
java full version "1.3beta-O"
tiffany>
(Review ID: 94362)
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