从框架按钮单击打开applet

Question

我在框架中有一个按钮。点击按钮后，applet将加载另一个框架。这些例外正在出现。Defg是我的applet类。有别的方法吗?谢谢。

     private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    // TODO add your handling code here:
     JApplet applet = new defg();
     // Send the applet an init() message.
     applet.init();
     // Construct a JFrame.
     final JFrame frame =
             new JFrame("FrameTitle");
     // Transfer the applet's context pane to the JFrame.
     frame.setContentPane(applet.getContentPane());
     // Transfer the applet's menu bar into the JFrame.
     // This line can be omitted if the applet
     // does not create a menu bar.
     frame.setJMenuBar(applet.getJMenuBar());
     // Make the application shut down when the user clicks
     // on the close button.
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     // Set the size of the frame.
     // To pack the frame as tightly as possible
     // replace the setSize() message with the following.
     // frame.pack();
     frame.setSize(800, 800);
     // Set the location of the frame.
     frame.setLocation(30, 30);
     // Show the frame.
     frame.setVisible(true);

}  

例外……

  Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at defg.init(defg.java:198)
at AppMain1.jButton1ActionPerformed(AppMain1.java:80)
at AppMain1.access$0(AppMain1.java:75)
at AppMain1$1.actionPerformed(AppMain1.java:40)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3320)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

Answer 1

问题出在applet的init方法中…

try { 
    java.awt.EventQueue.invokeAndWait(new Runnable() { 
        public void run() { 
            initComponents(); 
        } 
    }); 
} catch (Exception ex) { 
    ex.printStackTrace(); 
}

你不能在事件调度线程的上下文中调用invokeAndWait，因为这会产生死锁

相反，你想从事件调度线程外部调用init，然后，当加载时，加载UI的其余部分。

在这种情况下，SwingWorker可能是有用的，例如…

public class LoadAppletWorker extends SwingWorker<JApplet, JApplet> {
    @Override
    protected JApplet doInBackground() throws Exception {
        // TODO add your handling code here:
        JApplet applet = new defg();
        // Send the applet an init() message.
        applet.init();
        return applet;
    }
    @Override
    protected void done() {
        try {
            JApplet applet = get();
            // Construct a JFrame.
            final JFrame frame
                    = new JFrame("FrameTitle");
            // Transfer the applet's context pane to the JFrame.
            frame.setContentPane(applet.getContentPane());
            // Transfer the applet's menu bar into the JFrame.
            // This line can be omitted if the applet
            // does not create a menu bar.
            frame.setJMenuBar(applet.getJMenuBar());
            // Make the application shut down when the user clicks
            // on the close button.
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            // Set the size of the frame.
            // To pack the frame as tightly as possible
            // replace the setSize() message with the following.
            // frame.pack();
            frame.setSize(800, 800);
            // Set the location of the frame.
            frame.setLocation(30, 30);
            // Show the frame.
            frame.setVisible(true);
        } catch (InterruptedException | ExecutionException ex) {
            Logger.getLogger(Initapp.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

那么你可以使用类似于…

的东西来命名它

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    new LoadAppletWorker().execute();
}