需要在单击JFrame上的“退出”按钮时关闭JFrame

Need to close JFrame on clicking Exit button on JFrame

提问人：Afsal Baaqir A 提问时间：12/15/2021 最后编辑：TomerikooAfsal Baaqir A 更新时间：12/17/2021 访问量：88

问：

我正在创建一个简单的 Java 应用程序，我是 Java 的新手。请帮我解决这个问题

我正在使用 java 8，我正在尝试从一个帧移动到另一个帧，我可以这样做，但为此，我在代码中发生了一些异常，我无法弄清楚为什么以及那是什么

下面是我的代码，错误发生在下面给出。

package oops;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class HumanBenchmarkApp implements ActionListener{
    JFrame AppWindow, ReflexFrame, VisualFrame, CreditsFrame;
    JLabel Title;
    JButton Game1, Game2, Credits, Exit;
    public HumanBenchmarkApp(){
        AppWindow = new JFrame("Human Benchmark");
        AppWindow.setSize(400, 400);
        JPanel Content = new JPanel();
        Content.setBorder(new EmptyBorder(10, 10, 10, 10));
        Content.setLayout(new GridBagLayout());
        try{
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        }
        catch(Exception e){
            System.err.println(e.getMessage());
        }
        AppWindow.setLayout(new BoxLayout(AppWindow.getContentPane(),BoxLayout.Y_AXIS));
        Title = new JLabel("<html><h1><strong>Human Benchmark App</strong></h1><br></html>");
        Game1 = new JButton("<html><h4>Reflex Action Test</h4></html>");
        Game2 = new JButton("<html><h4>Visual Memory Test</h4></html>");
        Credits = new JButton("<html><h4>Credits</h4></html>");
        Exit = new JButton("<html><h4>Exit</h4></html>");
        Game1.addActionListener(this);
        Game2.addActionListener(this);
        Credits.addActionListener(this);
        Exit.addActionListener(this);
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        gbc.anchor = GridBagConstraints.NORTH;
        Content.add(Title, gbc);
        gbc.anchor = GridBagConstraints.CENTER;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        JPanel Buttons = new JPanel(new GridBagLayout());
        Buttons.add(Game1, gbc);
        Buttons.add(Game2, gbc);
        Buttons.add(Credits, gbc);
        Buttons.add(Exit, gbc);
        gbc.weighty = 1;
        Content.add(Buttons);
        AppWindow.add(Content);
        AppWindow.setVisible(true);
        AppWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public static void main(String[] args){
        new HumanBenchmarkApp();
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        JButton clicked = (JButton)e.getSource();
        if (clicked.getName().equals("Game1")){
            
        }
        else if(clicked.getName().equals("Game2")){
            
        }
        else if(clicked.getName().equals("Credits")){
            
        }
        else if(clicked.getName().equals("Exit")){
            System.exit(0);
        }
    }
}

这是我的代码，当我执行它时，我在 NetBeans 输出区域收到以下错误。

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at oops.HumanBenchmarkApp.actionPerformed(HumanBenchmarkApp.java:56)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    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:6539)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6304)
    at java.awt.Container.processEvent(Container.java:2239)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2297)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4535)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476)
    at java.awt.Container.dispatchEventImpl(Container.java:2283)
    at java.awt.Window.dispatchEventImpl(Window.java:2746)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
    at java.awt.EventQueue$4.run(EventQueue.java:733)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

错误在控制台上，JFrame 甚至没有关闭。

java swing nullpointerexception jframe

评论

0赞 VGR 12/16/2021
我很确定你应该使用而不是getName（）。getName（） 返回内部文本，该文本永远不会显示在窗口中，并且默认情况下为 null。也就是说，Agzam 的建议比使用一个大型 actionPerformed 方法要好。getText()
0赞 Afsal Baaqir A 12/16/2021
不，兄弟，我只需要内部文本才能在框架之间切换
1赞 Tomerikoo 12/16/2021
请不要通过破坏您的帖子为他人做更多工作。通过在 Stack Exchange 网络上发布，您已经根据 CC BY-SA 4.0 许可授予了 Stack Exchange 分发该内容的不可撤销权利（即无论您未来的选择如何）。根据 Stack Exchange 策略，帖子的未破坏版本是分发的版本。因此，任何破坏行为都将被恢复。如果您想了解更多关于删除帖子的信息，请参阅：删除工作原理？

答：

1赞 Agzam 12/15/2021 #1

我真的不明白为什么会有如此令人困惑的实现，如果你可以使用 lambda 表达式：ActionListener

        ...

        Game1.addActionListener(this);
        Game2.addActionListener(this);
        Credits.addActionListener(this);
        Exit.addActionListener(e -> {   // <---- NEW HERE
            System.exit(0);             // <---- NEW HERE
        });                             // <---- NEW HERE
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        gbc.anchor = GridBagConstraints.NORTH;
        Content.add(Title, gbc);
        gbc.anchor = GridBagConstraints.CENTER;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        JPanel Buttons = new JPanel(new GridBagLayout());

        ...

编辑：

或者你可以这样做：

Exit.addActionListener(new ActionListener() {
            
    @Override
    public void actionPerformed(ActionEvent arg0) {
        System.exit(0); 
    }
});

艺术 您不必比较名称，可以比较对象引用：

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

public class HumanBenchmarkApp implements ActionListener {
    
    JFrame appWindow, reflexFrame, visualFrame, creditsFrame;
    JLabel title;
    JButton game1, game2, credits, exit;
    
    public HumanBenchmarkApp() {
        appWindow = new JFrame("Human Benchmark");
        appWindow.setSize(400, 400);
        JPanel content = new JPanel();
        content.setBorder(new EmptyBorder(10, 10, 10, 10));
        content.setLayout(new GridBagLayout());
        try{
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        }
        catch(Exception e){
            System.err.println(e.getMessage());
        }
        appWindow.setLayout(new BoxLayout(appWindow.getContentPane(),BoxLayout.Y_AXIS));
        title = new JLabel("<html><h1><strong>Human Benchmark App</strong></h1><br></html>");
        game1 = new JButton("<html><h4>Reflex Action Test</h4></html>");
        game2 = new JButton("<html><h4>Visual Memory Test</h4></html>");
        credits = new JButton("<html><h4>Credits</h4></html>");
        exit = new JButton("<html><h4>Exit</h4></html>");
        game1.addActionListener(this);
        game2.addActionListener(this);
        credits.addActionListener(this);
        exit.addActionListener(this);
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        gbc.anchor = GridBagConstraints.NORTH;
        content.add(title, gbc);
        gbc.anchor = GridBagConstraints.CENTER;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        JPanel Buttons = new JPanel(new GridBagLayout());
        Buttons.add(game1, gbc);
        Buttons.add(game2, gbc);
        Buttons.add(credits, gbc);
        Buttons.add(exit, gbc);
        gbc.weighty = 1;
        content.add(Buttons);
        appWindow.add(content);
        appWindow.setVisible(true);
        appWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    
    public static void main(String[] args) {
        new HumanBenchmarkApp();
    }
    
    @Override
    public void actionPerformed(ActionEvent e) {
        JButton clicked = (JButton)e.getSource();
        if (clicked == game1) {

        }
        else if(clicked == game2) {

        }
        else if(clicked == credits) {

        }
        else if(clicked == exit) {
            System.exit(0);
        }
    }
}

评论

1赞 Extorc Productions 12/15/2021
完美！！！！
0赞 Afsal Baaqir A 12/16/2021
@Agzam我听说过 lambda 表达式，但我们的老师没有教我们这些，所以我用基本的简单实现来制作
0赞 Agzam 12/16/2021
@20CSE028 Afsal Baaqir A，我编辑了答案并添加了 2 个变体
0赞 Cheng Thao 12/17/2021 #2

问题是您的按钮 Exit 的名称不是“Exit”。这是您的代码：

Exit = new JButton("<html><h4>Exit</h4></html>");

相反，您可以比较 exit 和 clicked 是否引用了 Agzam 描述的相同按钮。

    @Override
    public void actionPerformed(ActionEvent e) {
        JButton clicked = (JButton)e.getSource();
        if (clicked == game1) {

        }
        else if(clicked == game2) {

        }
        else if(clicked == credits) {

        }
        else if(clicked == exit) {
            System.exit(0);
        }
    }

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