Question

这是我的追溯

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

我所有标记的事件都是

 jPanel1.removeAll();

第89行

 jButton1.addActionListener(new ActionListener() {

任何想法如何解决这个问题？我也在网上搜索找到任何帮助，但我没有找到任何东西。所有答案都表示赞赏。提前谢谢

Answer 1

你有没有初始化jButton1？由于NullPointerException出现在第89行，因此jButton1可能为null。可以肯定的是，只需尝试System.out.println(jButton1);，如果它打印出Null，则表示您没有正确初始化它。

我不知道是不是这样，但是如果是这样的话，请避免使用JButton jButton1 = null;之类的变量声明，而是使用JButton jButton1;，因为通过初始化一个带有null的变量，你会阻止编译器每当忘记初始化对象时都会发出警告。

Answer 2

你需要调试你的代码：

Basic Netbeans debuging

Debug Java Applications with Netbeans

尝试在netbeans上运行应用程序时出现java.lang.NullPointerException错误

2 个答案: