Java 基本textField actionListener出错(命令位于侦听器中时出错)
当我在文本字段上按enter键时,我不断收到错误(将在下面发布错误)。我希望文本字段将数据保存到全局定义的变量中。每当我在代码中不包含“name”时,actionListener就会工作,例如,如果我输入int a=3,那么就没有错误。我还全局声明了名称(在主gui上),因为如果我没有声明,我会得到一个错误,说变量不在范围内,这可能是一个问题Java 基本textField actionListener出错(命令位于侦听器中时出错),java,user-interface,jframe,actionlistener,jtextfield,Java,User Interface,Jframe,Actionlistener,Jtextfield,当我在文本字段上按enter键时,我不断收到错误(将在下面发布错误)。我希望文本字段将数据保存到全局定义的变量中。每当我在代码中不包含“name”时,actionListener就会工作,例如,如果我输入int a=3,那么就没有错误。我还全局声明了名称(在主gui上),因为如果我没有声明,我会得到一个错误,说变量不在范围内,这可能是一个问题 //Declared inside the main gui (the others are nested in this) JTextF
//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。因此,存在名称为
name
和namelab
的两个变量。构造函数将访问构造函数中声明的变量,因此GUI类的变量保持未初始化状态(null
)。ActionListener
访问GUI类中的变量,该变量为null
,并抛出NullPointerException
。你必须使用一个变量而不是两个。为了得到更准确的答案,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)。完美!我得到了它,谢谢,我把构造函数中的定义移到了GUI类中,它工作得非常好。