[英]Error with basic textField actionListener (Error when commands are in the listener)
当我在文本字段上按Enter时,我一直收到错误消息(以下将发帖错误)。 我希望文本字段将数据保存到全局定义的变量。 每当我的代码中不包含“名称”时,actionListener都可以工作,例如,如果我将int a = 3放入,则没有错误。 我也在全局上(在主gui上)声明了名称,因为如果我没有收到错误消息,指出变量不在范围内,也许这是一个问题吗?
//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.access$300(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:706)
at java.awt.EventQueue$3.run(EventQueue.java:704)
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:720)
at java.awt.EventQueue$4.run(EventQueue.java:718)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.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)
UI的组件定义了两次。 一次在GUI类中作为变量,一次在(我想)构造函数中。 由于这个nameLabel
存在名称为name
和nameLabel
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类的变量保持未初始化( null
)。 ActionListener
访问GUI类中的变量,该变量为null
并抛出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,我需要更多代码(或者至少比上面发布的摘录更有用)。
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