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更新：如果我将代码移动到 mouseclick 事件中（即，我没有调用 initMarksScreen()，而是直接将代码放入其中），它会按预期工作。所以我的问题是以自己的方法调用代码。这是否意味着如果我想在另一个点或另一个按钮上执行相同的步骤，我必须将代码直接放在那里而不是我可以调用的方法中？

我对 Java 相当陌生，并试图创建一个按钮来添加一个包含 JTable 的 JScrollPane。

它由以下方式调用：

    public void mouseClicked(java.awt.event.MouseEvent evt) {
            initMarksScreen();
        }

代码是：

public final void initMarksScreen() {
    String[] columnNames = {"Student ID",
                            "Last Name",
                            "Firstname",
                            "Status",
                            "Degree",
                            "Candidate No.",
                            "Stage",
                            "Year",
                            "Code",
                            "Title",
                            "Grade Mode",
                            "Mark",
                            "Result"};
    Object[][] data = {
            {"100123456", "Cooper","Sheldon", "Signed Up", "BSc Physics","1201234","1","12","PH1001","Blackholes and Revelations","D",new Integer(99),"P"},
            {"100123456", "Cooper","Sheldon", "Signed Up", "BSc Physics","1201234","1","12","PH1025","Astrophysics","D",new Integer(95),"P"}
        };
    JTable tMarks = new JTable(data, columnNames);
    JScrollPane scrollPane = new JScrollPane(tMarks);
    tMarks.setFillsViewportHeight(true);
    panelCentral.add(scrollPane); --!!ERROR AT THIS LINE!!
    panelCentral.revalidate();
}

面板声明为：

private static final Container panelCentral = null;

由于我对 Java 很陌生，我想有一个简单的修复方法，但如果我需要添加一个 SSCCE。

一切都显示正常，直到我单击按钮然后我得到的错误是：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at GUI.mainScreen.initMarksScreen(mainScreen.java:312)
at GUI.mainScreen$2.mouseClicked(mainScreen.java:183)
at java.awt.AWTEventMulticaster.mouseClicked(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
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1 回答 1

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如果panelCentral是 JPanel 并且它没有初始化，在添加之前初始化

 panelCentral = new JPanel();
 panelCentral.add(scrollPane);
于 2013-01-17T10:54:40.723 回答