Applet tile engine

I am not trying to make a game with an applet, just do some simple tile rendering things. I have come up with a nice effect, animated tiles too. The only problem is sometimes it loads in my browser and sometimes it does not. I am currenly using firefox, if I open the applet with ie it loads more often but still not all the time. I posted my full source and was wondering if someone can tell me why this is happening. Thanks.


import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class Tile_engine extends Applet implements KeyListener, Runnable {

  private int keyPressed = -1;
  private int screenX = 0;
  private int screenY = 0; 
  private final int TILE_MAX = 11;
  private final int TILE_SIZE = 32;
  private final int APPLET_WIDTH = 640;
  private final int APPLET_HEIGHT = 480; 
  private final int SKY = 0;
  private final int CLOUD_1 = 1;
  private final int CLOUD_2 = 2;
  private final int RED_BRICKS = 3;
  private final int GRASS = 4;
  private final int DIRT = 5;
  private final int STONE = 6;
  private final int QBOX1 = 7;
  private final int QBOX2 = 8;
  private final int QBOX3 = 9;
  private final int QBOX4 = 10;
  private final int MAP_ROWS = 15;
  private final int MAP_COLS = 65;
  private Image background = null;
  private Image buffer = null;
  private Graphics bgBuff;
  private Graphics bufferg;
  private Image[] tile = new Image[TILE_MAX];

  private final int map[][] = 
    {{0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,6,6,6,6,6,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0},
     {0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,7,7,7,7,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,6,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,7,0,0,0,0,0,0,0,0,0,0,0,0,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,3,3,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,3,3,3,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,6,6,6,6,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,0,0,0,0,0,0,0},
     {0,0,7,7,7,0,0,0,0,0,0,0,3,3,3,3,0,0,0,0,0,0,0,0,0,0,4,0,0,0,0,0,0,0,0,0,0,6,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,5,0,0,0,0,0,0,0,0,0,3,6,6,0,0,0,0,4,4,4,4,4,4,4,4,4,4,4,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,3,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,4,0,5,0,0,0,0,0,0,0,0,0,3,6,6,0,0,0,0,5,5,5,5,5,5,5,5,5,5,5,0,0,0,0,0,0,0,0,0,0,0},
     {4,4,4,4,4,4,4,4,0,0,4,4,4,4,4,4,4,4,4,4,4,4,0,0,5,0,5,0,0,4,4,4,0,0,0,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,4,4,4,4,6,6,6,4,4,4,4},
     {5,5,5,5,5,5,5,5,0,0,5,5,5,5,5,5,5,5,5,5,5,5,0,0,5,0,5,0,0,5,5,5,0,0,0,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,0,0,0,5,5,5,5}};
   
  
  public void init( ) {
    tile[SKY] = getImage(getDocumentBase(), "sky.png");
    tile[CLOUD_1] = getImage(getDocumentBase(), "cloud1.png");
    tile[CLOUD_2] = getImage(getDocumentBase(), "cloud2.png");
    tile[RED_BRICKS] = getImage(getDocumentBase(), "redBricks.png");
    tile[GRASS] = getImage(getDocumentBase(), "grass.png");
    tile[DIRT] = getImage(getDocumentBase(), "dirt.png");
    tile[STONE] = getImage(getDocumentBase(), "stone.png");
    tile[QBOX1] = getImage(getDocumentBase(), "qbox1.png");
    tile[QBOX2] = getImage(getDocumentBase(), "qbox2.png");
    tile[QBOX3] = getImage(getDocumentBase(), "qbox3.png");
    tile[QBOX4] = getImage(getDocumentBase(), "qbox4.png");

    buffer = createImage(TILE_SIZE * MAP_COLS, TILE_SIZE * MAP_ROWS);
    bufferg = buffer.getGraphics();

    addKeyListener(this); 

    if(buffer != null) {
      int tile_id;
      for(int y=0;y<MAP_ROWS;y++) {
        for(int x=0;x<MAP_COLS;x++) {
          tile_id = map[y][x]; 
          bufferg.drawImage(tile[tile_id], x * TILE_SIZE, y * TILE_SIZE, this);
        }
      }
    } 

  }

  public void start( ) {
    Thread th = new Thread(this);
    // start this thread
    th.start(); 
  }

  public void run( ) {
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
    while(true) {
      animate_tiles();
    
      try {
	Thread.sleep(200);
      } catch(InterruptedException ex) {
      }
      Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    } 
  }
  
  public void animate_tiles( ) {
    int tile_id;
    
    for(int y=0;y<MAP_ROWS;y++) {
      for(int x=0;x<MAP_COLS;x++) {
        tile_id = map[y][x]; 
      
        switch(tile_id) {
          case QBOX1: map[y][x] = QBOX2; break;
          case QBOX2: map[y][x] = QBOX3; break;
          case QBOX3: map[y][x] = QBOX4; break;
          case QBOX4: map[y][x] = QBOX1; break;
          default: break; //not needed  
        }
      }
    }
  }

  public void paint(Graphics g) {}

  public void update(Graphics g) {
    //animate_tiles();

    if(buffer != null) {
      int tile_id;
      for(int y=0;y<MAP_ROWS;y++) {
        for(int x=0;x<MAP_COLS;x++) {
          tile_id = map[y][x]; 
          bufferg.drawImage(tile[tile_id], x * TILE_SIZE, y * TILE_SIZE, this);
        }
      }
    } 

    paint(bufferg);
    g.drawImage(buffer, screenX, screenY, this); 
    repaint(); 
  }

  public void keyReleased( KeyEvent e ) { }
  public void keyPressed( KeyEvent e ) { }
  public void keyTyped( KeyEvent e ) {  
    char c = e.getKeyChar();
    if(c == 'z') { screenX+=5; }
    else if(c == 'c') { screenX-=5; }
  }  
}

you should post a more detailed description of the problem: does the applet stop with an error or is only nothing
visible? what does the java-console say (exception?) ?
my first guess is only that your loading several images in init() using no mediatracker or imageicon class. this can
lead to have some sideeffects of your applet, like images wont be displayed for quite a time while the programm is
yet running.