Java AWT-EventQueue-0 错误

Question

有人可以帮我调试这个吗

编辑1:错误不在下面的代码中*以下代码中出现错误:*

   if (e.getSource().equals(btnRefresh))
        {
            PeerList.removeAllElements();
            FileList.removeAllElements();


            try {
                AllPeers=(List <String>)Services.getPeers();
            } catch (RemoteException e1) {
                // TODO Auto-generated catch block

            }

            for (String CurrentPeer:AllPeers)
            {
                System.out.println(CurrentPeer);
                PeerList.addElement(CurrentPeer);
            }
        }

编辑 1:此处出现错误

lstPeerList.addListSelectionListener(new ListSelectionListener(){
            @Override
            public void valueChanged(ListSelectionEvent e) 
            {
                try 
                {
                    SelectedPeer=(String)lstPeerList.getSelectedValue();
                    List <String> PeerFiles=Services.getPeerFiles(SelectedPeer);
                    FileList.removeAllElements();
                    for (String CurrentFile:PeerFiles)
                    {
                        FileList.addElement(CurrentFile);
                    }
                } 
                catch (RemoteException e1) 
                {
                    // TODO Auto-generated catch block

                }
            }});

在下面的代码中，如果我按照以下代码检索变量，则会发生错误:

SelectedPeer=(String)lstPeerList.getSelectedValue();
List <String> PeerFiles=Services.getPeerFiles(SelectedPeer);

但是如果我这样做，即不使用检索到的变量，则不会发生错误:

SelectedPeer=(String)lstPeerList.getSelectedValue();
List <String> PeerFiles=Services.getPeerFiles("Noor");

没有发生错误，

异常(exception):

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at Server.getPeerFiles(Server.java:54)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:305)
        at sun.rmi.transport.Transport$1.run(Transport.java:159)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Transport.java:155)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:535)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:790)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:649)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:637)
        at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:255)
        at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:233)
        at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:142)
        at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:178)
        at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:132)
        at $Proxy0.getPeerFiles(Unknown Source)
        at MainForm$1.valueChanged(MainForm.java:55)
        at javax.swing.JList.fireSelectionValueChanged(JList.java:1765)
        at javax.swing.JList$ListSelectionHandler.valueChanged(JList.java:1779)
        at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:167)
        at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:147)
        at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:194)
        at javax.swing.DefaultListSelectionModel.removeIndexInterval(DefaultListSelectionModel.java:660)
        at javax.swing.plaf.basic.BasicListUI$Handler.intervalRemoved(BasicListUI.java:2589)
        at javax.swing.AbstractListModel.fireIntervalRemoved(AbstractListModel.java:161)
        at javax.swing.DefaultListModel.removeAllElements(DefaultListModel.java:385)
        at MainForm.actionPerformed(MainForm.java:223)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6267)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
        at java.awt.Component.processEvent(Component.java:6032)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4630)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2478)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

每次更改选择时都会调用 ListSelectionListener。这可能意味着现在没有选择，lstPeerList.getSelectedValue() 返回null。然后调用 getPeerFiles(null)，该方法似乎无法处理 null 参数。

您可以更改 getPeerFiles 方法，或者仅在所选值不为 null 时调用它。