Please, someone tell me what's wrong in this code...

Question

My MIDlet can't even start. So I think the problem is on GameCanvas class, 'couse is the only class I've changed before the game don't work. So I'll submit the code and you can see if find the error. Any sugestions will be apreciate.
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;
public class GameCanvasClass extends GameCanvas implements Runnable {
   private boolean playing;  
   // TiledLayer.
   private TiledLayer tiledCenary;
   // Layer.
   private LayerManager layer1 = new LayerManager();
   // Sprites.
   private CharacterClass player;
   private CharacterClass[] enemy;
   // Game settings;
   public static int gameLevel = 0;
   public static int numLives = 3;
   public static int numEnemies = 0;
   public static final int NUMBER_LEVELS = 10;
   public static boolean[] doneBuildLevel;
   /** Creates a new instance of GameCanvasClass */
   public GameCanvasClass() throws Exception {
      super(true);
      for(int i = 0; i < 10; i++)
         doneBuildLevel[i] = false;   
      Image image = Image.createImage("/bear.PNG");
      player = new CharacterClass(image, 16, 16, 16, 16);
      System.out.println("Public constructor started.");
   public void start() throws Exception {
      playing = true;
      Thread t = new Thread(this);
      t.start();
      System.out.println("start() method of Thread is on.");
   public void run() {
        try {
           setupGameLevel(gameLevel);
        catch(Exception e) {
           e.printStackTrace();
      Graphics g = getGraphics();
      while(playing == true) {
         drawGameScreen(g);
         checkCollision(numEnemies);
         checkInput();
         moveEnemies(numEnemies);
         try {
            Thread.sleep(15);
         catch(InterruptedException ie) {
   public void stop() {
      playing = false;      
   private void setupGameLevel(int level) throws Exception {
      if( (level == 0) && (doneBuildLevel[level] == false) ) {
         // Building cenary for the first level.
         tiledCenary = TiledLayerClass.buildTiledCenary(gameLevel);
         // Append to the layer.
         layer1.append(tiledCenary);
         layer1.append(player);
         doneBuildLevel[level] = true;
         numEnemies = 4;   // Setup 4 enemies for the first level.
         for(int i = 0; i < numEnemies; i++) {
            Image imagem = Image.createImage("/enemy1.PNG");  
            enemy[i] = new CharacterClass(imagem, 16, 16, 160, 32);
            layer1.append(enemy);
/* TODO
Change manually positions of all enemies,
since they start at the same position.
private void checkInput() {
int keyState = getKeyStates();
if(((keyState & UP_PRESSED) != 0) && (player.getPosY() > 16)) {
player.setLastPosY(player.getPosY());
player.setPosY(player.getPosY() - 1);
if(((keyState & DOWN_PRESSED) != 0) && (player.getPosY() < 208)) {
player.setLastPosY(player.getPosY());
player.setPosY(player.getPosY() + 1);
if(((keyState & RIGHT_PRESSED) != 0) && (player.getPosX() < 208)) {
player.setLastPosX(player.getPosX());
player.setPosX(player.getPosX() + 1);
if(((keyState & LEFT_PRESSED) != 0) && (player.getPosX() > 16)) {
player.setLastPosX(player.getPosX());
player.setPosX(player.getPosX() - 1);
/* Check collision of player against cenary, enemies, itens. Also check collision of all enemies against cenary.
Method must receive the number of enemies on the current level. */
private void checkCollision(int numberEnemies) {
if(player.collidesWith(tiledCenary, true)) {
player.setPosX(player.getLastPosX());
player.setPosY(player.getLastPosY());
for(int i = 0; i < numberEnemies; i++)
if(enemy[i].collidesWith(tiledCenary, true)) {
enemy[i].setPosX(enemy[i].getLastPosX());
enemy[i].setPosY(enemy[i].getLastPosY());
private void moveEnemies(int numberEnemies) {
for(int i = 0; i < numberEnemies; i++) {
if(enemy[i].getPosX() < 208) {
enemy[i].setLastPosX(enemy[i].getPosX());
enemy[i].setPosX(enemy[i].getPosX() + 1);
if(enemy[i].getPosX() > 16) {
enemy[i].setLastPosX(enemy[i].getPosX());
enemy[i].setPosX(enemy[i].getPosX() - 1);
private void drawGameScreen(Graphics g) {
g.fillRect(0, 0, 256, 256);
player.setPosition(player.getPosX(), player.getPosY());
for(int i = 0; i < numEnemies; i++)
enemy[i].setPosition(enemy[i].getPosX(), enemy[i].getPosY());
layer1.setViewWindow(player.getPosX() - 32, player.getPosY() - 32, 128, 110);
layer1.paint(g, 0, 0);
g.setColor(0, 0, 0);
flushGraphics();

Answer 1

Hi,
One thing that stroke me when I read your code is that you never allocate arrays
replace
private CharacterClass[] enemy;by
private CharacterClass[] enemy = new CharacterClass[MAX_ENEMIES];and
public static boolean[] doneBuildLevel;by
public static boolean[] doneBuildLevel = new boolean[NUMBER_LEVELS];Hope that help,
Jack