NPE may be thrown if JDesktopIcon is set to null on a JInternalFrame

Name: jl125535 Date: 03/17/2004


FULL PRODUCT VERSION :
java version "1.4.2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2-b28)
Java HotSpot(TM) Client VM (build 1.4.2-b28, mixed mode)

java version "1.5.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta2-b42)
Java HotSpot(TM) Client VM (build 1.5.0-beta2-b42, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows XP 5.1.2600

A DESCRIPTION OF THE PROBLEM :
The constructor of JInternalFrame invokes setVisible(false), which triggers events on the AWT event queue. If JInternalFrame.getDesktopPane is invoked in response to this event, a NullPointer exception will be thrown.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See attached code.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No exception should be thrown. It is arguably bad practice to put such side-effect-producing calls in the constructor (cf setText in JTextComponent).

ACTUAL -
java.lang.NullPointerException
        at javax.swing.JInternalFrame.getDesktopPane(JInternalFrame.java:1226)
        at JInternalFrameBug$Listener.eventDispatched(JInternalFrameBug.java:13)

        at java.awt.Toolkit$SelectiveAWTEventListener.eventDispatched(Toolkit.ja
va:2136)
        at java.awt.Toolkit.notifyAWTEventListeners(Toolkit.java:1988)
        at java.awt.Component.dispatchEventImpl(Component.java:3530)
        at java.awt.Container.dispatchEventImpl(Container.java:1627)
        at java.awt.Component.dispatchEvent(Component.java:3477)
        at java.awt.Container.addImpl(Container.java:675)
        at javax.swing.JInternalFrame.addImpl(JInternalFrame.java:446)
        at java.awt.Container.add(Container.java:518)
        at javax.swing.JInternalFrame.setRootPane(JInternalFrame.java:672)
        at javax.swing.JInternalFrame.<init>(JInternalFrame.java:273)
        at javax.swing.JInternalFrame.<init>(JInternalFrame.java:203)
        at JInternalFrameBug.main(JInternalFrameBug.java:25)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/** Demonstrates NPE when creating a JInternalFrame */
public class JInternalFrameBug {

    private static class Listener implements AWTEventListener {
        public void eventDispatched(AWTEvent e) {
            if (e.getSource() instanceof JInternalFrame) {
                try {
                    JInternalFrame f = (JInternalFrame)e.getSource();
                    JDesktopPane df = f.getDesktopPane();
                }
                catch(NullPointerException npe) {
                    npe.printStackTrace();
                    System.exit(1);
                }
            }
        }
    }

    public static void main(String[] args) {
        Toolkit.getDefaultToolkit().addAWTEventListener(new Listener(), -1);
        JInternalFrame f = new JInternalFrame();
        while (true)
            ;
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Catch the NPE when invoking JInternalFrame.getDesktopPane, or reimplement the function and check for a null pointer.
(Incident Review ID: 240158)
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