在safari中检测到internet explorer Java异常，但在IE中未检测到？

Question

我有一个java小程序代码，当它从IE打开时可以正常工作，但如果它是从Safari打开的，java控制台会产生一个nullpointerexception

生成此行为的代码如下所示：

public class MsgBoxPanel extends JDialog
{

  Panel panel1 = new Panel();
  JLabel label1 = new JLabel();
  JLabel label2 = new JLabel();

  public MsgBoxPanel() 
  {
     try 
     {
        jbInit();
     }
     catch(Exception e) 
     {
        e.printStackTrace();
     }
  }

  private void jbInit() throws Exception 
  {
     this.setBackground(Color.lightGray);
     this.setLayout(null);

     label1.setFont(common.COMPONENTS_FONT);
     label2.setFont(common.COMPONENTS_FONT);

     label2.setHorizontalAlignment(JLabel.CENTER);
     label2.setText("Buy");
     label2.setBounds(new Rectangle(0, -5, 400, 44));

     label1.setHorizontalAlignment(JLabel.CENTER);
     label1.setText("Are you sure?");
     label1.setBounds(new Rectangle(0, 0, 400, 44));

     panel1.setLayout(null);

     panel1.add(label1, null);
     panel1.add(label2, null);
  }

  public void setBounds(int x,int y,int width,int height)
  { 
      super.setBounds(x,y,width,height);
      this.setLayout(null);

     panel1.setBounds(4,6,this.getSize().width-8,this.getSize().height-12);

     this.add(panel1);

  }
}

当我从Safari（Mac OSX）调用小程序时，java控制台显示以下异常：

network: Created version ID: 1.8.0.45 network: Created version ID: 1.8.0.45 security: continue with running version network: Created version ID: 1.8.0.45 network: Created version ID: 1.8 network: Created version ID: 8.0.45 basic: exception: java.lang.reflect.InvocationTargetException. java.lang.RuntimeException: java.lang.reflect.InvocationTargetException at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.runOnEDTAndWait(Unknown Source) at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.instantiateApplet(Unknown Source) at sun.plugin2.applet.Plugin2Manager.initAppletAdapter(Unknown Source) at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) Caused by: java.lang.reflect.InvocationTargetException at com.sun.deploy.uitoolkit.impl.awt.OldPluginAWTUtil.invokeAndWait(Unknown Source) ... 5 more Caused by: java.lang.NullPointerException at mutajara.MsgBoxPanel.setBounds(Unknown Source) at java.awt.Component.move(Component.java:2101) at java.awt.Component.setLocation(Component.java:2090) at java.awt.Window.setLocation(Window.java:921) at java.awt.Window.init(Window.java:510) at java.awt.Window.<init>(Window.java:436) at java.awt.Window.<init>(Window.java:591) at java.awt.Dialog.<init>(Dialog.java:665) at java.awt.Dialog.<init>(Dialog.java:409) at javax.swing.JDialog.<init>(JDialog.java:272) at javax.swing.JDialog.<init>(JDialog.java:206) at javax.swing.JDialog.<init>(JDialog.java:154) at mutajara.MsgBoxPanel.<init>(Unknown Source) at mutajara.MainApplet.<init>(Unknown Source) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:422) at java.lang.Class.newInstance(Class.java:442) at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter$1.run(Unknown Source) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756) at java.awt.EventQueue.access$500(EventQueue.java:97) at java.awt.EventQueue$3.run(EventQueue.java:709) at java.awt.EventQueue$3.run(EventQueue.java:703) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86) at java.awt.EventQueue$4.run(EventQueue.java:731) at java.awt.EventQueue$4.run(EventQueue.java:729) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75) at java.awt.EventQueue.dispatchEvent(EventQueue.java:728) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) at java.awt.EventDispatchThread.run(EventDispatchThread.java:82) Ignored exception: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException basic: Dialog type is not candidate for embedding

Answer 1

当您在Java中扩展另一个类时，您的类属性（例如panel1）在超级构造函数完成后才初始化

我猜JDialog's构造的一部分涉及调用setBounds。您已经重写了此方法，因此该调用将命中被重写的setBounds。现在，由于JDialog仍处于构建阶段，您的panel1尚未创建和初始化。所以你得到了空指针异常

但你有更大的问题setBounds在运行时可以多次调用。您不希望每次都删除并重新添加面板。 我将把这些行从setBounds移到jbInit方法的顶部：

 this.setLayout(null);
 this.add(panel1);

---

更新

你可以保留你的面板。其中的挫折：

public void setBounds(int x,int y,int width,int height) { 
    super.setBounds(x,y,width,height);
    if (panel1 != null) {
       panel1.setBounds(4,6,this.getSize().width-8,this.getSize().height-12);
    }
}

或者，您可以使用LayoutManager让Swing为您定位组件，而不是自己定位组件：

//this.setLayout(null);
this.setLayout(new BorderLayout());
this.add(panel1);
// could use panel1.setBorder(...) to get your spacing around the outside