java.lang.NullPointerException bug when trying to run an app on netbeans

Question

Here is my traceback

Oct 9, 2012 3:58:44 PM org.jdesktop.application.Application$1 run
SEVERE: Application class sampleapp.SampeAppApp failed to launch
java.lang.NullPointerException
        at sampleapp.SampeAppView.<init>(MusicDownloaderView.java:89)
        at sampleapp.SampeAppApp.startup(MusicDownloaderApp.java:18)    
at org.jdesktop.application.Application$1.run(Application.java:171)
            at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
            at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:682)
            at java.awt.EventQueue.access$000(EventQueue.java:85)
            at java.awt.EventQueue$1.run(EventQueue.java:643)
            at java.awt.EventQueue$1.run(EventQueue.java:641)
            at java.security.AccessController.doPrivileged(Native Method)
            at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
            at java.awt.EventQueue.dispatchEvent(EventQueue.java:652)
            at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
            at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
            at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
            at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
            at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
            at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
    Exception in thread "AWT-EventQueue-0" java.lang.Error: Application class musicdownloader.MusicDownloaderApp failed to launch
            at org.jdesktop.application.Application$1.run(Application.java:177)
            at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
            at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:682)
            at java.awt.EventQueue.access$000(EventQueue.java:85)
            at java.awt.EventQueue$1.run(EventQueue.java:643)
            at java.awt.EventQueue$1.run(EventQueue.java:641)
            at java.security.AccessController.doPrivileged(Native Method)
            at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
            at java.awt.EventQueue.dispatchEvent(EventQueue.java:652)
            at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
            at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
            at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
            at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
            at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
            at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
    Caused by: java.lang.NullPointerException

also all my marked occurrences is

 jPanel1.removeAll();

Line 89 is

 jButton1.addActionListener(new ActionListener() {

Any ideas how to solve this ? I also searched online to find any help but i didn't found anything. All answers are appreciated. Thank you in advance

provide these lines please: sampleapp.SampeAppView.(MusicDownloaderView.java:89) at sampleapp.SampeAppApp.startup(MusicDownloaderApp.java:18) — Juvanis, Oct 09 '12 at 13:08
@AshokRaj how jPanel1 gives null? Could you explain it a bit more ? — Crystal Cruises, Oct 09 '12 at 13:10
the line 89 is jButton1.addActionListener(new ActionListener() { — Crystal Cruises, Oct 09 '12 at 13:11
The problem is in the constructor of `SampeAppView`. Perhaps you could post that? — David Grant, Oct 09 '12 at 13:13
show me what's @ sampleapp.SampeAppView.(MusicDownloaderView.java:89) — Ashok Raj, Oct 09 '12 at 13:14
Obviously `jButton1` is `null` at that particular moment. Check your initialisation. — Tim Lamballais, Oct 09 '12 at 13:22
how to check if is null? When i click on properties of jButton in action says null? must i remove it ? — Crystal Cruises, Oct 09 '12 at 13:26
It's really hard to advise you without any relevant source code. — Tim Lamballais, Oct 09 '12 at 13:28
i changed it from null to jButton1.action and i did not get back null on print out ...but the problem still exists — Crystal Cruises, Oct 09 '12 at 13:38

score 1 · Answer 1 · answered Oct 09 '12 at 13:27

Have you initialized jButton1? Since the NullPointerException occurs an line 89, jButton1 is probably null. To be sure, try simply System.out.println(jButton1);, if it prints out Null, it means you didn't initialize it correctly.

I don't know if it's the case, but if it is, avoid variable declarations like JButton jButton1 = null;, using JButton jButton1; instead, because by initializing a variable with null you're preventing the compiler to warn you whenever you forget to initialize an object.

score 0 · Answer 2 · answered Oct 09 '12 at 13:31

0

You need to DEBUG your code:

Basic Netbeans debuging

Debug Java Applications with Netbeans

answered Oct 09 '12 at 13:31

raspayu

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java.lang.NullPointerException bug when trying to run an app on netbeans

2 Answers2