Name: gm110360 Date: 02/13/2004


FULL PRODUCT VERSION :
java version "1.4.1_02"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_02-b06)
Java HotSpot(TM) Client VM (build 1.4.1_02-b06, mixed mode)

FULL OS VERSION :
Microsoft Windows 2000 [Version 5.00.2195]

A DESCRIPTION OF THE PROBLEM :
Here is a comparison of the source code for VetoableChangeSupport and PropertyChangeSupport

First PropertyChangeSupport
/**
     * Add a PropertyChangeListener to the listener list.
     * The listener is registered for all properties.
     *
     * @param listener The PropertyChangeListener to be added
     */
    public synchronized void addPropertyChangeListener(
PropertyChangeListener listener) {

if (listener instanceof PropertyChangeListenerProxy) {
PropertyChangeListenerProxy proxy =
                   (PropertyChangeListenerProxy)listener;
// Call two argument add method.
addPropertyChangeListener(proxy.getPropertyName(),
                    (PropertyChangeListener)proxy.getListener());
} else {
if (listeners == null) {
listeners = new java.util.Vector();
}
listeners.addElement(listener);
}
    }
Now VetoableChangeSupport
/**
     * Add a VetoableListener to the listener list.
     * The listener is registered for all properties.
     *
     * @param listener The VetoableChangeListener to be added
     */

    public synchronized void addVetoableChangeListener(
VetoableChangeListener listener) {
        if (listener instanceof VetoableChangeListenerProxy) {
            VetoableChangeListenerProxy proxy =
                    (VetoableChangeListenerProxy)listener;
            // Call two argument add method.
            addVetoableChangeListener(proxy.getPropertyName(),
                    (VetoableChangeListener)proxy.getListener());
        } else {
            if (listeners == null) {
                listeners = new java.util.Vector();
            }
        }
        listeners.addElement(listener);
    }

Notice the different location of listeners.addElement(listener);
In the veto version, listeners has not been initialised. The first time you try to add a VetoableChangeListenerProxy, listeners is null, therefore a NullPointerException is caused when trying to addElement

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
initialise a VetoableChangeSupport object and add a ListenerProxy as above

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Expected result is to be the same as adding PropertyChangeListenerProxy to PropertyChangeSupport
ACTUAL -
NullPointerException

ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.lang.NullPointerException
        at java.beans.VetoableChangeSupport.addVetoableChangeListener(VetoableChangeSupport.java:65)
        at uk.co.capacitas.smart.network.ChangeAdapter.addListener(NetworkElement.java:428)
        at uk.co.capacitas.smart.network.NetworkElement.addListener(NetworkElement.java:251)
        at uk.co.capacitas.smart.network.CompositeNetworkElement.addComponent(CompositeNetworkElement.java:100)
        at uk.co.capacitas.smart.network.NetworkNode.addNodeInterface(NetworkNode.java:229)
        at uk.co.capacitas.smart.network.NetworkBuilder.addNetworkSiteService(NetworkBuilder.java:71)
        at uk.co.capacitas.smart.network.ConcreteNetworkManager.addNetworkSiteService(ConcreteNetworkManager.java:141)
        at uk.co.capacitas.smart.testharness.TestBuilder.addSites(TestBuilder.java:234)
        at uk.co.capacitas.smart.testharness.TestBuilder.buildNetwork(TestBuilder.java:101)
        at uk.co.capacitas.smart.testharness.TestBuilder.buildNetwork(TestBuilder.java:121)
        at uk.co.capacitas.smart.testharness.TestHarness.build(TestHarness.java:51)
        at uk.co.capacitas.smart.testharness.TestHarnessTest.testRun(TestHarnessTest.java:50)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at uk.co.capacitas.smart.testharness.TestHarnessTest.main(TestHarnessTest.java:26)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.beans.*;

public class Tester {
    
    public Tester() {
    }
    
    public static void main(String[] args) {
        Tester tester = new Tester();
        VetoableChangeSupport changeSupport = new VetoableChangeSupport(tester);
        
        VetoableChangeListener listener = new VetoableChangeListener(){
            public void vetoableChange(PropertyChangeEvent e) {
            
            }
        };
        VetoableChangeListenerProxy proxy = new VetoableChangeListenerProxy("property",listener);
        changeSupport.addVetoableChangeListener(proxy);
        
    }
    
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Not using a proxy works fine
(Incident Review ID: 185508)
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