package manyballs;import javax.microedition.lcdui.*;/** * A SmallBall is a lightweight animated ball that runs in it's own thread. * It moves within a rectangular region, bouncing off the walls. */class SmallBall implements Runnable {        // random number generator        static java.util.Random random = new java.util.Random();        // controls the speed of all balls; delay in centiseconds        static int delay = 20;        static void slower() {                delay += 10;                if (delay > 100) delay = 100;        }        static void faster() {                delay -= 10;                if (delay < 0) delay = 0;        }        // the matrix to transform the direction based on the        // current direction and which wall was hit        static int[][] matrix = {                {  1, -1,  -1, 1,   1, 1 },                { -1, -1,   1, 1,  -1, 1 },                null,                {  1, 1,  -1, -1,   1, -1 },                { -1, 1,   1, -1,  -1, -1 }        };        // the region in which the ball moves        int top, left, width, height;        // the position and radius of the ball        int posX, posY;        int radius = 5, ballSize = radius*2;        // the direction of the ball is controlled by these two variables        int deltaX;        int deltaY;        // a handle onto the singleton Graphics object        Graphics g;        Canvas canvas;        // public variables to control the behaviour of the thread        public boolean stop;        /**         * Constructor defines the region in which the ball moves as well         * as its starting position.         */        SmallBall(Canvas c, int left, int top, int width, int height) {                super();                canvas = c;                this.left = left + 1;                this.top  = top + 1;                this.width = width - (2 * radius + 2);                this.height = height - (2 * radius + 2);                // use positive random #s                this.posX = (random.nextInt()>>>1) % (this.width-20) + 10;                this.posY = (random.nextInt()>>>1) % (this.height-20) + 10;                deltaX = random.nextInt() & 1;                deltaY = random.nextInt() & 1;                if (deltaX == 0) deltaX = -1;                if (deltaY == 0) deltaY = -1;        }        /**         * Starts the ball running.         */        public void run() {            //	    System.out.println("starting... " + this);                int right = left + width;                int bottom = top + height;                stop = false;                while (!stop) {                        ballSize = radius * 2;                        // calculate a direction of the ball                        // as an integer in the range                        // -2 .. 2 (excluding 0)                        int direction = deltaX + deltaY;                        if (direction == 0) direction = deltaX + 2*deltaY;                        // is the current position colliding with any wall                        int collision = 0;                        if (posX <= left || posX >= right) collision++;                        if (posY <= top || posY >= bottom) collision += 2;                        // change the direction appropriately                        // if there was a collision                        if (collision != 0) {                                collision = (collision - 1) * 2;                                deltaX = matrix[direction+2][collision];                                deltaY = matrix[direction+2][collision+1];                        }                        // calculate the new position and queue a repaint                        posX = posX + deltaX;                        posY = posY + deltaY;                        canvas.repaint(posX - 1, posY - 1,                                       ballSize + 2, ballSize + 2);                        // use the delay to control the speed of the ball                        try {                                Thread.sleep(delay);                        } catch (InterruptedException e) {}                }        }    /**     * Paint the ball.     */    void paint(Graphics g) {        g.setColor(255,0,0);//----------ball color        g.fillArc(posX, posY, ballSize, ballSize, 0, 360);    }    boolean inside(int x1, int y1, int x2, int y2) {        return (posX <= x2)            && (posY <= y2)            && ((posX + ballSize) >= x1)            && ((posY + ballSize) >= y1);    }    public String toString() {        return super.toString() + " x = " + posX + ", y = " + posY;    }}