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Java Swing 文本域错误

转载 作者:行者123 更新时间:2023-11-29 06:39:03 25 4
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我是 Java 和 Java Swing 的新手,我无法让它工作。我有 2 个文本字段,需要通过单击按钮将 textfield1 中的文本传递到 te textfield2,但它经常崩溃。

代码如下:

package javaapplication7;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;


public class JavaApplication7 {

public static void main(String[] args) {
JFrame theFrame = new JFrame();
theFrame.setTitle("Title");
theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
theFrame.setSize(400, 400);
theFrame.setLocation(400, 400);

theFrame.setContentPane(new Paneel());
theFrame.setVisible(true);
}
}

class Paneel extends JPanel{
JButton button1;
JTextField field1;
JTextField field2;


public Paneel(){
JButton button1 = new JButton("Click");
button1.addActionListener(new KH());
add(button1);

JTextField field1 = new JTextField(10);
add(field1);

JTextField field2 = new JTextField(10);
add(field2);
}


class KH implements ActionListener{
@Override
public void actionPerformed(ActionEvent e){
field2.setText(field1.getText());
}
}
}

当我运行它时,它给出了一个巨大的错误列表,有人知道吗?

错误列表:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javaapplication7.Paneel$KH.actionPerformed(JavaApplication7.java:54)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
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:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
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)

最佳答案

您当前隐藏Paneel 中的变量button1field1field2 >,即您正在 Paneel 的构造函数中创建这些组件的 local 实例,但具有这些名称的类成员变量仍然是 null,导致NPE

通过删除 JButtonJTextField 类型关键字,您可以将组件分配给预期的类成员变量:

public Paneel(){
button1 = new JButton("Click");
...
field1 = new JTextField(10);
...
field2 = new JTextField(10);
...
}

关于Java Swing 文本域错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15209128/

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