ArrayIndexOutOfBoundsException with ActionListener in JList

Question

我看了其他看起来与我有关的问题，但它们并没有“解决”我的问题。我收到了 ArrayIndexOutOfBoundsException，我正在处理的代码正在删除 JList 中名为 contactList 的“联系人”。

我已经实现了一个按钮，该按钮将简单地删除联系人列表中的“联系人”。程序应该做的是，如果按钮删除“广播”，这是联系人列表中的第一个元素，将通过输出显示消息返回错误。否则，它应该简单地从联系人列表中删除联系人。

我现在遇到的问题是，它在删除联系人时会产生arrayIndexOutOfBoundsExc，不仅如此，它还会打印出其他if语句中的错误行。删除广播会输出错误消息，但仍会显示arrary IndexOutofBoundsExc的异常。

另外，我不确定我是否正确执行了第一个 if 语句。我在开头包含了必要的代码以及测试代码后遇到的错误。

private JList<String> listContacts;
listContacts = new JList<String>(controller.getContacts());
// gets contact list from controller class which gets contact list from client class.
private JButton btDeleteUser;

JButton deleteUser = new JButton("Delete User");

deleteUser.addActionListener(new MyButtonListener5());

class MyButtonListener5 implements ActionListener{
    public void actionPerformed(ActionEvent e){
        DefaultListModel<String> list = (DefaultListModel)(listContacts.getModel());
        String contact = listContacts.getSelectedValue();
        int j = -1;
        for(int i = list.getSize()-1; i >= 0; i--){
            if(list.getElementAt(i).equals("Broadcast")){
                controller.displayMsg("[ERROR] You cannot delete broadcast\n");
            }
            else if(list.getElementAt(i).equals(contact) && i != j){
                j = i;
            }
        }
        if(j != -1){
            (DefaultListModel)list.remove(j);
        }
    }
}

[java] Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: javax.swing.JList$4 cannot be cast to javax.swing.DefaultListModel
 [java]     at edu.ucsb.cs56.projects.networking.chat.chatclient.view.ClientWindow$MyButtonListener5.actionPerformed(ClientWindow.java:391)
 [java]     at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
 [java]     at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
 [java]     at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
 [java]     at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
 [java]     at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
 [java]     at java.awt.Component.processMouseEvent(Component.java:6535)
 [java]     at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
 [java]     at java.awt.Component.processEvent(Component.java:6300)
 [java]     at java.awt.Container.processEvent(Container.java:2236)
 [java]     at java.awt.Component.dispatchEventImpl(Component.java:4891)
 [java]     at java.awt.Container.dispatchEventImpl(Container.java:2294)
 [java]     at java.awt.Component.dispatchEvent(Component.java:4713)
 [java]     at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
 [java]     at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
 [java]     at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
 [java]     at java.awt.Container.dispatchEventImpl(Container.java:2280)
 [java]     at java.awt.Window.dispatchEventImpl(Window.java:2750)
 [java]     at java.awt.Component.dispatchEvent(Component.java:4713)
 [java]     at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
 [java]     at java.awt.EventQueue.access$500(EventQueue.java:97)
 [java]     at java.awt.EventQueue$3.run(EventQueue.java:709)
 [java]     at java.awt.EventQueue$3.run(EventQueue.java:703)
 [java]     at java.security.AccessController.doPrivileged(Native Method)
 [java]     at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
 [java]     at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
 [java]     at java.awt.EventQueue$4.run(EventQueue.java:731)
 [java]     at java.awt.EventQueue$4.run(EventQueue.java:729)
 [java]     at java.security.AccessController.doPrivileged(Native Method)
 [java]     at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
 [java]     at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
 [java]     at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
 [java]     at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
 [java]     at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
 [java]     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
 [java]     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
 [java]     at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Answer 1

基础知识：

如果 JList 中有 5 个元素，则最后一个元素的索引将为 4，列表的大小将为 5。

问题：

 for(int i = 0; i <= list.getSize(); i++){

在这里，您说从 0 循环槽到列表的大小（包括列表的大小），因此当我达到列表的长度时，您将尝试获取具有相同索引的元素，而该元素不存在。

你需要改变