keyboardeventdemo.java

此源码为机械工业出版社出版的《Java语言程序设计》第三版所配套的书中所有源代码。

// KeyboardEventDemo.java: Receive key input
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class KeyboardEventDemo extends JApplet
{
  private KeyboardPanel keyboardPanel = new KeyboardPanel();

  // Main method used if run as an application
  public static void main(String[] args)
  {
    // Create a frame
    JFrame frame = new JFrame("KeyboardEvent Demo");

    // Create an instance of the applet
    KeyboardEventDemo applet = new KeyboardEventDemo();

    // Add the applet instance to the frame
    frame.getContentPane().add(applet, BorderLayout.CENTER);

    // Invoke init() and start()
    applet.init();
    applet.start();

    // Display the frame
    frame.setSize(300, 300);
    // frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

    // Set focus on the keyboardPanel
    applet.focus();
  }

  // Initialize UI
  public void init()
  {
    // Add the keyboard panel to accept and display user input
    getContentPane().add(keyboardPanel);

    // Request focus
    focus();

  }

  // Set focus on the panel
  public void focus()
  {
    // It is required for receiving key input
    keyboardPanel.requestFocus();
  }
}

// KeyboardPanel for receiving key input
class KeyboardPanel extends JPanel implements KeyListener
{
  private int x = 100;
  private int y = 100;
  private char keyChar = 'A'; // Default key

  public KeyboardPanel()
  {
    addKeyListener(this); // Register listener
  }

  public void keyReleased(KeyEvent e)
  {
  }

  public void keyTyped(KeyEvent e)
  {
  }

  public void keyPressed(KeyEvent e)
  {
    switch (e.getKeyCode())
    {
      case KeyEvent.VK_DOWN: y += 10; break;
      case KeyEvent.VK_UP: y -= 10; break;
      case KeyEvent.VK_LEFT: x -= 10; break;
      case KeyEvent.VK_RIGHT: x += 10; break;
      default: keyChar = e.getKeyChar();
    }
    repaint();
  }

  // Draw the character
  public void paintComponent(Graphics g)
  {
    super.paintComponent(g);

    g.setFont(new Font("TimesRoman", Font.PLAIN, 24));
    g.drawString(String.valueOf(keyChar), x, y);
  }
}