MIDP2.0手机上手电筒程序的实现

　　可以在所有支持MIDP2.0版本的手机上运行的手电筒程序。程序实现的原理是：利用Display对象来实现对于手机背景等的控制，在该系列的手机中只能实现闪烁背景灯的功能。

　　实现代码如下：
//文件名：LightMIDlet.java

package light;

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

public class LightMIDlet extends MIDlet {
  static LightMIDlet instance;
  LightForm displayable = new LightForm(this);
  public LightMIDlet() {
    instance = this;
  }

  public void startApp() {
    Display.getDisplay(this).setCurrent(displayable);
  }

  public void pauseApp() {
  }

  public void destroyApp(boolean unconditional) {
  }

  public static void quitApp() {
    instance.destroyApp(true);
    instance.notifyDestroyed();
    instance = null;
  }

}

//文件名：LightForm.java

package light;

import javax.microedition.lcdui.*;

public class LightForm extends Form implements CommandListener {
  StringItem si;
  Command cmdOpen;
  Command cmdClose;
  Command cmdExit;
  Display display;
  public LightForm(LightMIDlet lm) {
    super("手电筒");
    si = new StringItem("手电筒状态：","打开");
    this.append(si);

    display = Display.getDisplay(lm);

    cmdOpen = new Command("打开",Command.OK,1);
    this.addCommand(cmdOpen);

    cmdClose = new Command("关闭",Command.CANCEL,1);
    this.addCommand(cmdClose);

    cmdExit = new Command("退出",Command.EXIT,1);
    this.addCommand(cmdExit);

    setCommandListener(this);

    boolean b;

    b = display.flashBacklight(1000000);

    if(b == false){
      Alert alert = new Alert("手电筒","您的手机不支持该功能!",null,AlertType.INFO);
      alert.setTimeout(3000);
      display.setCurrent(alert);
    }
  }

  public void commandAction(Command c, Displayable d) {
    //关闭
    if (c == cmdExit) {
      // stop the MIDlet
      LightMIDlet.quitApp();
    }
    //打开
    if(c == cmdOpen){
      display.flashBacklight(1000000);
      si.setText("打开");
    }

    if(c == cmdClose){
      display.flashBacklight(0);
      si.setText("关闭");
    }
  }

}