按向下箭头键启动程序,首先观察字符串.这里看一下这个示例程序：

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class KeyBindingExample

{

private void createAndDisplayGUI()

{

JFrame frame = new JFrame("Key Binding Example");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

DrawingPanel contentPane = new DrawingPanel();

frame.setContentPane(contentPane);

frame.pack();

frame.setLocationByPlatform(true);

frame.setVisible(true);

contentPane.requestFocusInWindow();

}

public static void main(String... args)

{

SwingUtilities.invokeLater(new Runnable()

{

public void run()

{

new KeyBindingExample().createAndDisplayGUI();

}

});

}

}

class DrawingPanel extends JPanel

{

private int x;

private int y;

private String[] commands = {

"UP",

"DOWN",

"LEFT",

"RIGHT"

};

private ActionListener panelAction = new ActionListener()

{

@Override

public void actionPerformed(ActionEvent ae)

{

String command = (String) ae.getActionCommand();

if (command.equals(commands[0]))

y -= 1;

else if (command.equals(commands[1]))

y += 1;

else if (command.equals(commands[2]))

x -= 1;

else if (command.equals(commands[3]))

x += 1;

repaint();

}

};

public DrawingPanel()

{

x = 0;

y = 0;

for (int i = 0; i < commands.length; i++)

registerKeyboardAction(panelAction,

commands[i],

KeyStroke.getKeyStroke(commands[i]),

JComponent.WHEN_IN_FOCUSED_WINDOW);

}

@Override

public Dimension getPreferredSize()

{

return (new Dimension(500, 300));

}

@Override

public void paintComponent(Graphics g)

{

super.paintComponent(g);

String displayText = "X : " + x + " and Y : " + y;

System.out.println(displayText);

g.drawString(displayText, x, y);

}

}