[英]Error with basic textField actionListener (Error when commands are in the listener)
當我在文本字段上按Enter時,我一直收到錯誤消息(以下將發帖錯誤)。 我希望文本字段將數據保存到全局定義的變量。 每當我的代碼中不包含“名稱”時,actionListener都可以工作,例如,如果我將int a = 3放入,則沒有錯誤。 我也在全局上(在主gui上)聲明了名稱,因為如果我沒有收到錯誤消息,指出變量不在范圍內,也許這是一個問題嗎?
//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的組件定義了兩次。 一次在GUI類中作為變量,一次在(我想)構造函數中。 由於這個nameLabel
存在名稱為name
和nameLabel
兩個變量。 構造函數將訪問在構造函數中聲明的變量,因此GUI類的變量保持未初始化( null
)。 ActionListener
訪問GUI類中的變量,該變量為null
並拋出NullPointerException
。 您必須使用一個變量而不是兩個。 為了獲得更准確的答案,我需要更多代碼(或者至少比上面發布的摘錄更有用)。
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