timerdemo.java

一个j2me手机编程程序

package ch09.section02;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;

public class TimerDemo
    extends MIDlet {
  Display display;
  StarField field = new StarField();
  FieldMover mover = new FieldMover();
  Timer timer = new Timer();
  public TimerDemo() {
    display = Display.getDisplay(this);
  }

  protected void destroyApp(boolean unconditional) {
  }

  protected void startApp() {
    display.setCurrent(field);
//时间延迟100毫秒
    timer.schedule(mover, 100, 100);
  }

  protected void pauseApp() {
  }

  public void exit() {
    //停止滚动退出应用程序
    timer.cancel();
    destroyApp(true);
    notifyDestroyed();
  }

  //该类实现动画
  class FieldMover
      extends TimerTask {
    public void run() {
      field.scroll();
    }
  }

  class StarField
      extends Canvas {
    //定义星空显示区域
    int height;
    int width;
    int[] stars;

//随即产生星星数量
    Random generator = new Random();
    boolean painting = false;
    public StarField() {
      height = getHeight();
      width = getWidth();
      stars = new int[height];
      for (int i = 0; i < height; ++i) {
        stars[i] = -1;
      }
    }

    //实现区域连续向下滚动
    public void scroll() {
      if (painting) {
        return;
      }
      for (int i = height - 1; i > 0; --i) {
        stars[i] = stars[i - 1];
      }
      stars[0] = (generator.nextInt() %
                  (3 * width)) / 2;
      if (stars[0] >= width) {
        stars[0] = -1;
      }
      repaint();
    }

    protected void paint(Graphics g) {
      painting = true;
      g.setColor(0, 0, 0);
      g.fillRect(0, 0, width, height);
      g.setColor(255, 255, 255);
      for (int y = 0; y < height; ++y) {
        int x = stars[y];
        if (x == -1) {
          continue;
        }
        //绘制一个简单星星，以一条短线代表
        g.drawLine(x, y, x, y);
      }
      painting = false;
    }

    protected void keypressed(int keycode) {
      exit();
    }
  }
}