Animation Midlet

<strong>J2ME in a Nutshell</strong>
<strong>By Kim Topley</strong>
<strong>ISBN: 0-596-00253-X</strong>


<strong>import java.util.Timer;</strong>
<strong>import java.util.TimerTask;</strong>
<strong>import javax.microedition.lcdui.Canvas;</strong>
<strong>import javax.microedition.lcdui.Command;</strong>
<strong>import javax.microedition.lcdui.CommandListener;</strong>
<strong>import javax.microedition.lcdui.Display;</strong>
<strong>import javax.microedition.lcdui.Displayable;</strong>
<strong>import javax.microedition.lcdui.Form;</strong>
<strong>import javax.microedition.lcdui.Gauge;</strong>
<strong>import javax.microedition.lcdui.Graphics;</strong>
<strong>import javax.microedition.lcdui.Item;</strong>
<strong>import javax.microedition.lcdui.ItemStateListener;</strong>
<strong>import javax.microedition.midlet.MIDlet;</strong>

<strong>public class AnimationMIDlet extends MIDlet </strong>
<strong> implements CommandListener, ItemStateListener {</strong>

<strong>// The MIDlet’s Display object</strong>
<strong> private Display display;</strong>

<strong>// Flag indicating first call of startApp</strong>
<strong> protected boolean started;</strong>

<strong>// Exit command</strong>
<strong> private Command exitCommand;</strong>

<strong>// Setup command</strong>
<strong> private Command setupCommand;</strong>

<strong>// Run command</strong>
<strong> private Command runCommand;</strong>

<strong>// Configuration form</strong>
<strong> private Form form;</strong>

<strong>// Animation canvas</strong>
<strong> private AnimationCanvas canvas;</strong>

<strong>// Gauge for block count</strong>
<strong> private Gauge blockGauge;</strong>

<strong>// Gauge for frame rate</strong>
<strong> private Gauge rateGauge;</strong>

<strong>// Initial frame rate</strong>
<strong> private static final int FRAME_RATE = 1;</strong>

<strong>// Initial number of blocks</strong>
<strong> private static final int BLOCK_COUNT = 1;</strong>

<strong>protected void startApp() {</strong>
<strong> if (!started) {</strong>
<strong> display = Display.getDisplay(this);</strong>
<strong> form = new Form(”Animation”);</strong>
<strong> rateGauge = new Gauge(”Frame rate”, true, 10, FRAME_RATE);</strong>
<strong> blockGauge = new Gauge(”Blocks”, true, 4, BLOCK_COUNT);</strong>
<strong> form.append(rateGauge);</strong>
<strong> form.append(blockGauge);</strong>
<strong> form.setItemStateListener(this);</strong>

<strong>canvas = createAnimationCanvas();</strong>

<strong>exitCommand = new Command(”Exit”, Command.EXIT, 0);</strong>
<strong> setupCommand = new Command(”Setup”, Command.SCREEN, 0);</strong>
<strong> runCommand = new Command(”Run”, Command.SCREEN, 0);</strong>

<strong> canvas.addCommand(setupCommand);</strong>
<strong> form.addCommand(exitCommand);</strong>
<strong> form.addCommand(runCommand);</strong>

<strong> canvas.setCommandListener(this);</strong>

<strong> started = true;</strong>
<strong> }</strong>
<strong> }</strong>

<strong>protected void pauseApp() {</strong>
<strong> }</strong>

<strong>protected void destroyApp(boolean unconditional) {</strong>
<strong> }</strong>

<strong>public void commandAction(Command c, Displayable d) {</strong>
<strong> if (c == exitCommand) {</strong>
<strong> // Exit. No need to call destroyApp</strong>
<strong> // because it is empty.</strong>
<strong> notifyDestroyed();</strong>
<strong> } else if (c == runCommand) {</strong>
<strong> display.setCurrent(canvas);</strong>
<strong> } else if (c == setupCommand) {</strong>
<strong> display.setCurrent(form);</strong>
<strong> }</strong>
<strong> }</strong>

<strong>public void itemStateChanged(Item item) {</strong>
<strong> if (item == blockGauge) {</strong>
<strong> int count = blockGauge.getValue();</strong>
<strong> if (count &lt; 1) {</strong>
<strong> count = 1;</strong>
<strong> }</strong>
<strong> canvas.setBlockCount(count);</strong>
<strong> } else if (item == rateGauge) {</strong>
<strong> int count = rateGauge.getValue();</strong>
<strong> if (count &lt; 1) {</strong>
<strong> count = 1;</strong>
<strong> }</strong>
<strong> canvas.setFrameRate(count);</strong>
<strong> } </strong>
<strong> }</strong>

<strong>// Creates the canvas that will draw the block</strong>
<strong> protected AnimationCanvas createAnimationCanvas() {</strong>
<strong> return new AnimationCanvas();</strong>
<strong> }</strong>

<strong>class AnimationCanvas extends Canvas {</strong>

<strong>// Size of each block</strong>
<strong> protected static final int SIZE = 4;</strong>

<strong>// Initial speeds in the X direction</strong>
<strong> protected final int[] xSpeeds = { 2, -2, 0, -2 };</strong>

<strong>// Initial speeds in the Y direction</strong>
<strong> protected final int[] ySpeeds = { 2, -2, 2, -0 };</strong>

<strong>// Background color</strong>
<strong> protected int background = display.isColor() ? 0 : 0xc0c0c0;</strong>

<strong>// Foreground color</strong>
<strong> protected int foreground = display.isColor() ? 0xffff00 : 0;</strong>

<strong>// Width of screen</strong>
<strong> protected int width = getWidth();</strong>

<strong>// Height of screen</strong>
<strong> protected int height = getHeight();</strong>

<strong>// The screen update rate</strong>
<strong> protected int frameRate;</strong>

<strong>// The blocks to draw on the screen</strong>
<strong> protected Block[] blocks;</strong>

<strong>// The update timer</strong>
<strong> protected Timer timer;</strong>

<strong>// The update timer task</strong>
<strong> protected TimerTask updateTask;</strong>

<strong>// Gets the maximum number of blocks</strong>
<strong> public int getMaxBlocks() {</strong>
<strong> return blocks.length;</strong>
<strong> }</strong>

<strong>// Constructs a canvas with default settings</strong>
<strong> AnimationCanvas() {</strong>
<strong> setBlockCount(BLOCK_COUNT);</strong>
<strong> setFrameRate(FRAME_RATE);</strong>
<strong> }</strong>

<strong>// Sets the number of blocks to draw</strong>
<strong> public void setBlockCount(int count) {</strong>
<strong> if (count &gt; xSpeeds.length) {</strong>
<strong> throw new IllegalArgumentException(”Cannot have more than ” </strong>
<strong> + xSpeeds.length + ” blocks”);</strong>
<strong> }</strong>

<strong>blocks = new Block[count];</strong>
<strong> createBlocks();</strong>
<strong> }</strong>

<strong>// Gets the number of blocks to draw</strong>
<strong> public int getBlockCount() {</strong>
<strong> return blocks.length;</strong>
<strong> }</strong>

<strong>// Sets the number of updates per second</strong>
<strong> public void setFrameRate(int frameRate) {</strong>
<strong> if (frameRate &lt; 1 || frameRate &gt; 10) {</strong>
<strong> throw new IllegalArgumentException(”Frame rate must be &gt; 0 and &lt;= 10″);</strong>
<strong> }</strong>
<strong> this.frameRate = frameRate;</strong>
<strong> if (isShown()) {</strong>
<strong> startFrameTimer();</strong>
<strong> }</strong>
<strong> }</strong>

<strong>// Gets the number of updates per second</strong>
<strong> public int getFrameRate() {</strong>
<strong> return frameRate;</strong>
<strong> }</strong>

<strong>// Paint canvas background and all</strong>
<strong> // of the blocks in their correct locations.</strong>
<strong> protected void paint(Graphics g) {</strong>
<strong> // Paint with the background color</strong>
<strong> g.setColor(background);</strong>
<strong> g.fillRect(0, 0, width, height);</strong>

<strong>// Draw all of the blocks</strong>
<strong> g.setColor(foreground);</strong>
<strong> synchronized (this) {</strong>
<strong> for (int i = 0, count = blocks.length; i &lt; count; i++) {</strong>
<strong> g.fillRect(blocks[i].x, blocks[i].y, SIZE, SIZE);</strong>
<strong> }</strong>
<strong> }</strong>
<strong> }</strong>

<strong>// Notification that the canvas has been made visible</strong>
<strong> protected void showNotify() {</strong>
<strong> // Start the frame timer running</strong>
<strong> startFrameTimer();</strong>
<strong> }</strong>

<strong>// Notification that the canvas is no longer visible</strong>
<strong> protected void hideNotify() {</strong>
<strong> // Stop the frame timer </strong>
<strong> stopFrameTimer();</strong>
<strong> }</strong>

<strong>// Creates the blocks to be displayed</strong>
<strong> private void createBlocks() {</strong>
<strong> int startX = (width – SIZE)/2;</strong>
<strong> int startY = (height – SIZE)/2;</strong>
<strong> for (int i = 0, count = blocks.length; i &lt; count; i++) {</strong>
<strong> blocks[i] = new Block(startX, startY, xSpeeds[i], ySpeeds[i]);</strong>
<strong> }</strong>
<strong> }</strong>

<strong>// Starts the frame redraw timer</strong>
<strong> protected void startFrameTimer() {</strong>
<strong> timer = new Timer();</strong>

<strong>updateTask = new TimerTask() {</strong>
<strong> public void run() {</strong>
<strong> moveAllBlocks();</strong>
<strong> }</strong>
<strong> };</strong>
<strong> long interval = 1000/frameRate;</strong>
<strong> timer.schedule(updateTask, interval, interval);</strong>
<strong> }</strong>

<strong>// Stops the frame redraw timer</strong>
<strong> protected void stopFrameTimer() {</strong>
<strong> timer.cancel(); </strong>
<strong> }</strong>

<strong>// Called on expiry of timer.</strong>
<strong> public synchronized void moveAllBlocks() {</strong>
<strong> // Update the positions and speeds</strong>
<strong> // of all of the blocks</strong>
<strong> for (int i = 0, count = blocks.length; i &lt; count; i++) {</strong>
<strong> blocks[i].move();</strong>

<strong>// Request a repaint of the screen</strong>
<strong> repaint(); </strong>
<strong> }</strong>
<strong> }</strong>

<strong>// Inner class used to represent a block on the screen</strong>
<strong> class Block {</strong>
<strong> int x; // X position</strong>
<strong> int y; // Y position</strong>
<strong> int xSpeed; // Speed in the X direction</strong>
<strong> int ySpeed; // Speed in the Y direction</strong>

<strong>Block(int x, int y, int xSpeed, int ySpeed) {</strong>
<strong> this.x = x;</strong>
<strong> this.y = y;</strong>
<strong> this.xSpeed = xSpeed;</strong>
<strong> this.ySpeed = ySpeed;</strong>
<strong> }</strong>

<strong>void move() {</strong>
<strong> x += xSpeed;</strong>
<strong> if (x &lt;= 0 || x + SIZE &gt;= width) {</strong>
<strong> xSpeed = -xSpeed;</strong>
<strong> }</strong>

<strong>y += ySpeed;</strong>
<strong> if (y &lt;= 0 || y + SIZE &gt;= height) {</strong>
<strong> ySpeed = -ySpeed;</strong>
<strong> } </strong>
<strong> } </strong>
<strong> }</strong>
<strong> }</strong>

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