SPRite，精靈，顧名思義，專用來代表游戲中的動畫角色，比如飛機，坦克等等。在MIDP1.0中，我們必須自己寫專門的類來實現Sprite，幸運的是，MIDP2.0為Sprite提供了強力支持，可以創建靜態，動態，不透明和透明的Sprite，下面我們預備在上次的GameCanvas基礎上添加一個Sprite并讓它動起來。

Sprite的主要構造方法有：

Sprite(Image)：構造一個單幅圖案的Sprite；

Sprite(Image, int width, int height)：構造一個動畫Sprite，圖片將按照指定大小被分為N個Frame，通過setFrame(int index)就可以讓Sprite動起來。我們用了一個有透明背景的png圖片創建坦克的Sprite：

（注重這個圖是放大的JPG格式，你需要用photoshop之類的軟件處理成有透明背景的png格式，大小為64x16）

我們在Eclipse中建立如下工程和目錄：

以下是畫出Sprite的TankGameCanvas.java：

package tank.midp.core;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;

public class TankGameCanvas extends GameCanvas implements Runnable {
    // 控制方向：
    private static int INDEX_OF_UP = 0;
    private static int INDEX_OF_DOWN = 1;
    private static int INDEX_OF_LEFT = 3;
    private static int INDEX_OF_RIGHT = 2;

    private boolean isPlay; // Game Loop runs when isPlay is true
    private long delay; // To give thread consistency
    private int currentX, currentY; // To hold current position of the 'X'
    private int width; // To hold screen width
    private int height; // To hold screen height

    private Sprite spriteTank; // our sprite!

    // Constructor and initialization
    public TankGameCanvas() {
        super(true);
        width = getWidth();
        height = getHeight();
        currentX = width / 2;
        currentY = height / 2;
        delay = 20;
        // init sprite:
        try {
            Image image = Image.createImage("/res/img/player1.png"); // 注重路徑
            spriteTank = new Sprite(image, 16, 16); // 大小是16x16
        }
        catch(Exception e) { e.printStackTrace(); }
    }

    // Automatically start thread for game loop
    public void start() {
        isPlay = true;
        new Thread(this).start();
    }

    public void stop() { isPlay = false; }

    // Main Game Loop
    public void run() {
        Graphics g = getGraphics();
        while (isPlay) {
            input();
            drawScreen(g);
            try {
                Thread.sleep(delay);
            }
            catch (InterruptedException ie) {}
        }
    }

    // Method to Handle User Inputs
    private void input() {
        int keyStates = getKeyStates();
        // Left
        if ((keyStates & LEFT_PRESSED) != 0) {
            currentX = Math.max(0, currentX - 1);
            spriteTank.setFrame(INDEX_OF_LEFT);
        }
        // Right
        if ((keyStates & RIGHT_PRESSED) !=0 ) {
            if ( currentX + 5 < width)
                currentX = Math.min(width, currentX + 1);
            spriteTank.setFrame(INDEX_OF_RIGHT);
        }
        // Up
        if ((keyStates & UP_PRESSED) != 0) {
            currentY = Math.max(0, currentY - 1);
            spriteTank.setFrame(INDEX_OF_UP);
        }
        // Down
        if ((keyStates & DOWN_PRESSED) !=0) {
            if ( currentY + 10 < height)
                currentY = Math.min(height, currentY + 1);
            spriteTank.setFrame(INDEX_OF_DOWN);
        }
    }
    // Method to Display Graphics
    private void drawScreen(Graphics g) {
        g.setColor(0); // black
        g.fillRect(0, 0, getWidth(), getHeight());

        // 畫一個Sprite非常簡單：
        spriteTank.setPosition(currentX, currentY);
        spriteTank.paint(g);

        flushGraphics();
    }
}