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

Question

这是我的回溯

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

我所有标记的事件也是

 jPanel1.removeAll();

第 89 行是

 jButton1.addActionListener(new ActionListener() {

有什么想法可以解决这个问题吗？我还在网上搜索以寻求任何帮助，但没有找到任何内容。所有答案均表示赞赏。 预先感谢您

Answer 1

你初始化了jButton1吗？ 由于 NullPointerException 发生在第 89 行，因此 jButton1 可能为 null。 可以肯定的是，简单地尝试一下System.out.println(jButton1);，如果打印出Null，则意味着您没有正确初始化它。

我不知道是否是这种情况，但如果是这样，请避免像 JButton jButton1 = null; 这样的变量声明，而是使用 JButton jButton1; ，因为用 null 初始化变量会阻止编译器在您忘记初始化对象时发出警告。