Java 事件监听

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) {

  }
}