Java 事件监听

 

 

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package com.gibe;   import javax.swing.*; import java.awt.*; import java.awt.event.KeyEvent; import java.awt.event.KeyListener;   public class Listen extends JFrame {   private MyPanel panel = null;     public static void main(String[] args) {     Listen listen = new Listen();   }     public Listen() {     panel = new MyPanel(10, 10);     this.add(panel);     this.setSize(400, 500);     this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);     this.setVisible(true);     // 窗口JFrame可监听键盘事件     this.addKeyListener(panel);   } }   // MyPanel画板可绘制圆,KeyListener可监听键盘事件 class MyPanel extends JPanel implements KeyListener {   // 把左上角坐标(x,y)设置变量   private int x;   private int y;     public MyPanel(int x, int y) {     this.x = x;     this.y = y;   }     @Override   public void paint(Graphics g) {     super.paint(g);     g.fillOval(x, y, 20, 20);   }     //有字符输出时，该方法就会触发   @Override   public void keyTyped(KeyEvent e) {     }     @Override   public void keyPressed(KeyEvent e) { //    System.out.println((char)e.getKeyCode()+"pressed");     switch (e.getKeyCode()) {       case KeyEvent.VK_DOWN:         ++y;         break;       case KeyEvent.VK_UP:         --y;         break;       case KeyEvent.VK_LEFT:         --x;         break;       case KeyEvent.VK_RIGHT:         ++x;         break;       default:         System.out.println(e.getKeyChar() + " ignored");     }     // 画板重绘     this.repaint();   }     //当某个键释放(松开)，该方法会触发   @Override   public void keyReleased(KeyEvent e) {     } }