i'm sure you must know about this one by now, but here goes:

when trying to open a java file which does not have an accompanying form, you
get the following exceptions:

Tue Feb 27 18:55:49 EST 2001java.lang.NullPointerException: null
Annotation: Exception occurred in Request Processor
org.openide.util.RequestProcessor$Holder(task org.netbeans.core.ModuleActions$1@
2669d5 [-50, 1])
        at org.openide.util.RequestProcessor$Task.createHolder(RequestProcessor.
java:275)
        at org.openide.util.RequestProcessor.post(RequestProcessor.java:99)
        at org.openide.util.RequestProcessor.post(RequestProcessor.java:72)
        at org.netbeans.core.ModuleActions.invokeAction(ModuleActions.java:89)
        at org.openide.explorer.view.TreeView$ClickAdapter.mouseClicked(TreeView
.java:773)
        at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:21
1)
        at java.awt.Component.processMouseEvent(Component.java:3718)
        at java.awt.Component.processEvent(Component.java:3544)
        at java.awt.Container.processEvent(Container.java:1164)
        at java.awt.Component.dispatchEventImpl(Component.java:2593)
        at java.awt.Container.dispatchEventImpl(Container.java:1213)
        at java.awt.Component.dispatchEvent(Component.java:2497)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:2451
)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:2230)

        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:2125)
        at java.awt.Container.dispatchEventImpl(Container.java:1200)
        at java.awt.Window.dispatchEventImpl(Window.java:914)
        at java.awt.Component.dispatchEvent(Component.java:2497)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:339)
        at java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:10
3)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
[catch] at java.awt.EventDispatchThread.run(EventDispatchThread.java:84)

Tue Feb 27 18:55:49 EST 2001java.lang.NullPointerException: null
java.lang.NullPointerException
        at javax.swing.plaf.basic.BasicTextUI.modelChanged(BasicTextUI.java:467)

        at javax.swing.plaf.basic.BasicTextUI$UpdateHandler.propertyChange(Basic
TextUI.java:1518)
        at javax.swing.event.SwingPropertyChangeSupport.firePropertyChange(Swing
PropertyChangeSupport.java:161)
        at javax.swing.event.SwingPropertyChangeSupport.firePropertyChange(Swing
PropertyChangeSupport.java:130)
        at javax.swing.JComponent.firePropertyChange(JComponent.java:3198)
        at org.openide.text.QuietEditorPane.firePropertyChange(QuietEditorPane.j
ava:37)
        at javax.swing.text.JTextComponent.setDocument(JTextComponent.java:323)
        at org.openide.text.CloneableEditor.initialize(CloneableEditor.java:219)

        at org.openide.text.CloneableEditor.<init>(CloneableEditor.java:117)
        at org.openide.text.EditorSupport$Editor.<init>(EditorSupport.java:513)
        at org.openide.text.EditorSupport$Editor.<init>(EditorSupport.java:505)
        at org.netbeans.modules.java.JavaEditor$JavaEditorComponent.<init>(JavaE
ditor.java:962)
        at org.netbeans.modules.java.JavaEditor.createJavaEditorComponent(JavaEd
itor.java:883)
        at org.netbeans.modules.java.JavaEditor.createCloneableTopComponent(Java
Editor.java:875)
        at org.openide.windows.CloneableOpenSupport.openCloneableTopComponent(Cl
oneableOpenSupport.java:142)
        at org.openide.windows.CloneableOpenSupport.open(CloneableOpenSupport.ja
va:61)
        at org.openide.actions.OpenAction.performAction(OpenAction.java:72)
        at org.openide.util.actions.NodeAction.actionPerformed(NodeAction.java:7
9)
        at org.netbeans.core.ModuleActions$1.run(ModuleActions.java:76)
        at org.openide.util.Task.run(Task.java:124)
[catch] at org.openide.util.RequestProcessor$ProcessorThread.run(RequestProcesso
r.java:562)

as of yet i have found no way to open these java files in the ide.