timerdemo.java

Alert和Timer编程范例

/* TimerDemo.java
 * This is a simple example of a MIDlet that uses a timer to perform a simple simulation of a moving starfield.
 * The stars are drawn as points using low-level graphics APIs. 
 */
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 );
    timer.schedule( mover, 100, 100 );
  }

  protected void pauseApp() { }

  public void exit(){
    timer.cancel(); // stop scrolling
    destroyApp( true );
    notifyDestroyed();
  }

class FieldMover extends TimerTask {
  public void run(){
    field.scroll();
  }
}

class StarField extends Canvas {
  int        height;
  int        width;
  int[]      stars;
  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;
    }
  }

  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;

      g.drawLine( x, y, x, y );
    }

    painting = false;
  }

  protected void keyPressed( int keyCode ){
    exit();
  }
}
}