基本 textField actionListener 出错（命令在侦听器中时出错）

Question

当我在我的文本字段上按回车键时，我不断收到错误消息（下面会出现 post 错误）。我希望文本字段将数据保存到全局定义的变量中。每当我的代码中不包含 'name' 时，actionListener 就会工作，例如，如果我输入 int a = 3 则不会出现错误。我还全局声明了名称（在主 gui 上），因为如果我不这样做，我会收到一条错误消息，提示变量不在范围内，这可能是个问题？

    //Declared inside the main gui (the others are nested in this)
    JTextField name;
    JLabel nameLabel;

    //Name text field defined inside the gui jInternalFrame
    TextField name = new TextField("Enter Name..", 20);
    JLabel nameLabel = new JLabel();
    nameLabel.setText("Name: ");
    name.addActionListener(new nameListener());
    addRoomPanel.add(nameLabel);
    addRoomPanel.add(name);`

    //ActionListener defined outside of the text field gui
    class nameListener implements ActionListener{
        public void actionPerformed(ActionEvent e){
            nameString = name.getText();
            name.setText("saved");
            name.selectAll();
         }
    }

ERROR MESSAGE:
    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at InternalFrame$dobListener.actionPerformed(InternalFrame.java:445)
    at java.awt.TextField.processActionEvent(TextField.java:617)
    at java.awt.TextField.processEvent(TextField.java:585)
    at java.awt.Component.dispatchEventImpl(Component.java:4872)
    at java.awt.Component.dispatchEvent(Component.java:4698)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:747)
    at java.awt.EventQueue.access0(EventQueue.java:103)
    at java.awt.EventQueue.run(EventQueue.java:706)
    at java.awt.EventQueue.run(EventQueue.java:704)
    at java.security.AccessController.doPrivileged(Native Method)
    at  java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue.run(EventQueue.java:720)
    at java.awt.EventQueue.run(EventQueue.java:718)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:717)
    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

UI 的组件定义了两次。一次在 GUI-class 作为变量，一次在（我想）构造函数中。因此存在名称为 name 和 nameLabel 的两个变量。构造函数将访问在构造函数中声明的变量，因此 GUI-class 的变量保持未初始化状态 (null)。 ActionListener 访问 GUI-class 中的变量，即 null 并抛出一个 NullPointerException。您必须使用一个变量而不是两个。为了获得更准确的答案，我需要更多的代码（或者至少比上面发布的代码片段更有用）。

基本 textField actionListener 出错（命令在侦听器中时出错）

Error with basic textField actionListener (Error when commands are in the listener)

java

user-interface

jframe

actionlistener

jtextfield