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java – JApplet和KeyListener

2019-07-18 08:03:30 作者：互联网

我正在为我的计算机科学课开发一个应用程序.任务是编写计算器,但不使用JTextFields或JTextAreas.我想出了实现KeyListener的想法,它在appletviewer和JFrame中都运行良好,但在Google Chrome(可能还有其他浏览器)中根本不起作用.

这是我的代码片段.

//- BinaryCalc.java
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;

public class BinaryCalc extends JApplet implements KeyListener {

    private JPanel panel;

    public BinaryCalc() {
        super();

        panel = new JPanel();
        this.add(panel);

        panel.addKeyListener(this);
        panel.requestFocusInWindow();
    }

    @Override
    public void init() {
        JOptionPane.showMessageDialog(this, "applet");
        panel.setFocusable(true);
        panel.requestFocus();
    }

    public void keyPressed(KeyEvent e) {
        JOptionPane.showMessageDialog(this, (char) e.getKeyCode());
    }

    public void keyReleased(KeyEvent e) {}

    public void keyTyped(KeyEvent e) {}

    public JPanel getPanel() { return panel; }

    public static void main(String args[]) {
        JFrame frame = new JFrame("Binary Calculator");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setMinimumSize(new Dimension(320, 240));

        BinaryCalc kalkulator = new BinaryCalc();
        frame.add(kalkulator);

        frame.pack();
        frame.setVisible(true);
        kalkulator.getPanel().requestFocusInWindow();
    }

}

和包含我的applet的HTML文件.

<!doctype html>
<html>

<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <link rel="stylesheet" type="text/css" href="style.css">
    <title>Kalkulator binarny</title>
</head>

<body>
    <div style="text-align: center; border-bottom: 1px solid black">
        <h1>Kalkulator Binarny</h1>
    </div>

    <br/>
    <object style="display: block; margin: auto;" type="application/x-java-applet" width="320" height="240">
    <param name="code" value="BinaryCalc.class" />
    <!--- <param name="archive" value="Liczba.jar" /> -->
        What a terrible failure: applet failed to load!
    </object>   
    <br/>
</body>

</html>

有任何想法吗？

解决方法:

>使用KeyBindings而不是KeyListener
>不要为JApplet创建自己的JFrame,只需在applet实例上调用getContentPane()并在那里添加所有组件.
>所有组件都应该在包含在SwingUtilities#invokeAndWait(..)块中的JApplet覆盖init()方法中创建
> JApplets和Applet没有main(..)方法(除了测试目的)
>使用requestFocusInWindow()而不是requestFocus()

我强烈建议你阅读：

> How to Make Applets
> JApplet tutorial

这是一个适合我的例子.它只是将一个不可编辑的JTextField添加到JPanel,然后将KeyEvent.VK_0和KeyEvent.VK_1的KeyBindings添加到JPanel.如果用户键入0或1,它将显示在不可编辑的JTextField中：

import java.awt.BorderLayout;
import java.awt.event.*;
import java.lang.reflect.InvocationTargetException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;

public class BinaryCalc extends JApplet {

    private JTextField jtf;

    @Override
    public void init() {
        try {
            SwingUtilities.invokeAndWait(new Runnable() {
                @Override
                public void run() {

                    JPanel panel = new JPanel();
                    setKeyBindings(panel);
                    jtf = new JTextField(10);
                    //so we cant edited it without pressing a key
                    jtf.setEditable(false);

                    panel.add(jtf);
                    getContentPane().add(panel, BorderLayout.CENTER);
                    panel.requestFocusInWindow();//incase we lost focus
                }
            });
        } catch (InterruptedException ex) {
            Logger.getLogger(BinaryCalc.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InvocationTargetException ex) {
            Logger.getLogger(BinaryCalc.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    private void setKeyBindings(final JPanel panel) {
        panel.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(KeyEvent.VK_0,0), "0");
        panel.getActionMap().put("0", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                String tmp = jtf.getText();
                jtf.setText(tmp + "0");
            }
        });
        panel.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(KeyEvent.VK_1,0), "1");
        panel.getActionMap().put("1", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                String tmp = jtf.getText();
                jtf.setText(tmp + "1");
            }
        });
    }
}

标签：java,swing,jframe,keylistener,japplet
来源： https://codeday.me/bug/20190718/1494374.html