一样，canvas在动画向前滚动以后自动被重画(repaint)。不过这样的实现办法是可选的，
你可以这样做，也可以让程序选择合适的时候重画canvas。

因为MIDP 1.0不支持透明的图片，AnimatedImage 类使用一个剪辑列表来模拟透明的效果，剪辑列表是图片被剪成的方块
区域的系列。图片被画出来的时候分开几次，每次画一个剪辑列表里面的剪辑区域。剪辑列表在帧的基础上被定义好，所以
你需要为图片的每一帧创建一个数组。数组的大小应该是4的倍数，因为每一个剪辑面积保持了四个数值：左坐标，顶坐标，
宽度以及高度。坐标的原点是整个图片的左上角。需要注意的是使用了剪辑列表会使动画慢下来。如果图片更加复杂的话，你应该
使用矢量图片。

AnimatedImage类扩展了java.util.TimerTask，允许你设定一个timer。这里有个例子说明如何使用timer做动画：
Timer timer = new Timer();
AnimatedImage ai = ..... // get the image
timer.schedule( ai, 200, 200 );

每隔大约200毫秒，timer调用AnimatedImage.run()方法一次，这个方法使得动画翻滚到下一个帧。现在我们需要的是让MIDlet
来试试显示动画！我们定义一个简单的Canvas类的子类，好让我们把动画“粘贴上去”。
import java.util.*;
import javax.microedition.lcdui.*;

// A canvas to which you can attach one or more
// animated images. When the canvas is painted,
// it cycles through the animated images and asks
// them to paint their current image.

public class AnimatedCanvas extends Canvas {;
private Display display;
private Image offscreen;
private Vector images = new Vector();

public AnimatedCanvas( Display display ){;
this.display = display;

// If the canvas is not double buffered by the
// system, do it ourselves...

if( !isDoubleBuffered() ){;
offscreen = Image.createImage( getWidth(),
getHeight() );
};
};

// Add an animated image to the list.

public void add( AnimatedImage image ){;
images.addElement( image );
};

// Paint the canvas by erasing the screen and then
// painting each animated image in turn. Double
// buffering is used to reduce flicker.

protected void paint( Graphics g ){;
Graphics saved = g;

if( offscreen != null ){;
g = offscreen.getGraphics();
};

g.setColor( 255, 255, 255 );
g.fillRect( 0, 0, getWidth(), getHeight() );

int n = images.size();
for( int i = 0; i < n; ++i ){;
AnimatedImage img = (AnimatedImage)
images.elementAt( i );
img.draw( g );
};

if( g != saved ){;
saved.drawImage( offscreen, 0, 0,
Graphics.LEFT | Graphics.TOP );
};
};
};
AnimatedCanvas 类的代码相当简单，由一个动画导入方法和一个paint方法。canvas画布每次被画，背景都会被擦除
然后循环每个导入的AnimatedImage对象，直接画到自己身上来（自己扩展了canvas类）。

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

// MIDlet that displays some simple animations.
// Displays a series of birds on the screen and
// animates them at different (random) rates.

public class AnimationTest extends MIDlet
implements CommandListener {;

private static final int BIRD_FRAMES = 7;
private static final int NUM_BIRDS = 5;

private Display display;
private Timer timer = new Timer();
private AnimatedImage[] birds;
private Random random = new Random();

public static final Command exitCommand =
new Command( "Exit",
Command.EXIT, 1 );

public AnimationTest(){;
};

public void commandAction( Command c,
Displayable d ){;
if( c == exitCommand ){;
exitMIDlet();
};
};

protected void destroyApp( boolean unconditional )
throws MIDletStateChangeException {;
exitMIDlet();
};

public void exitMIDlet(){;
timer.cancel(); // turn it off...
notifyDestroyed();
};

// Generate a non-negative random number...

private int genRandom( int upper ){;
return( Math.abs( random.nextInt() ) % upper );
};

public Display getDisplay(){; return display; };

// Initialize things by creating the canvas and then
// creating a series of birds that are moved to
// random locations on the canvas and attached to
// a timer for scheduling.

protected void initMIDlet(){;
try {;
AnimatedCanvas c = new
AnimatedCanvas( getDisplay() );
Image[] images =
loadFrames( "/images/bird",
BIRD_FRAMES );

int w = c.getWidth();
int h = c.getHeight();

birds = new AnimatedImage[ NUM_BIRDS ];
for( int i = 0; i < NUM_BIRDS; ++i ){;
AnimatedImage b = new
AnimatedImage( c, images );
birds =