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PONullpointerexception in Browser but not AppletViewer
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<p>Before I begin, I know I should be using Swing rather than AWT, but this is what the book I'm using teaches with, so I'm just going with it for now.</p> <p>Now, my question is why the AppletViewer runs this code just fine, but every browser I've tried (Chrome, Firefox, IE) throws the following error:</p> <pre><code>java.lang.NullPointerException at ImageEntity.load(ImageEntity.java:61) at GalacticWar.init(GalacticWar.java:55) at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.init(Unknown Source) at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source) at java.lang.Thread.run(Unknown Source) </code></pre> <hr> <h2><strong>GalacticWar.java</strong></h2> <pre><code>/***************************************************** * Beginning Java Game Programming, 2nd Edition * by Jonathan S. Harbour * GALACTIC WAR, Chapter 11 *****************************************************/ import java.applet.*; import java.awt.*; import java.awt.event.*; import java.awt.geom.*; import java.awt.image.*; import java.util.*; /***************************************************** * Primary class for the game *****************************************************/ public class GalacticWar extends Applet implements Runnable, KeyListener { //the main thread becomes the game loop Thread gameloop; //use this as a double buffer BufferedImage backbuffer; //the main drawing object for the back buffer Graphics2D g2d; //toggle for drawing bounding boxes boolean showBounds = false; //create the asteroid array int ASTEROIDS = 20; Asteroid[] ast = new Asteroid[ASTEROIDS]; //create the bullet array int BULLETS = 10; Bullet[] bullet = new Bullet[BULLETS]; int currentBullet = 0; //the player's ship ImageEntity ship = new ImageEntity(this); //create the identity transform AffineTransform identity = new AffineTransform(); //create a random number generator Random rand = new Random(); /***************************************************** * applet init event *****************************************************/ public void init() { //create the back buffer for smooth graphics backbuffer = new BufferedImage(640, 480, BufferedImage.TYPE_INT_RGB); g2d = backbuffer.createGraphics(); //set up the ship ship.setX(320); ship.setY(240); ship.load("spaceship1.png"); ship.setGraphics(g2d); //set up the bullets for (int n = 0; n<BULLETS; n++) { bullet[n] = new Bullet(); } //set up the asteroids for (int n = 0; n<ASTEROIDS; n++) { ast[n] = new Asteroid(); ast[n].setRotationVelocity(rand.nextInt(3)+1); ast[n].setX((double)rand.nextInt(600)+20); ast[n].setY((double)rand.nextInt(440)+20); ast[n].setMoveAngle(rand.nextInt(360)); double ang = ast[n].getMoveAngle() - 90; ast[n].setVelX(calcAngleMoveX(ang)); ast[n].setVelY(calcAngleMoveY(ang)); } //start the user input listener addKeyListener(this); } /***************************************************** * applet update event to redraw the screen *****************************************************/ public void update(Graphics g) { //start off transforms at identity g2d.setTransform(identity); //erase the background g2d.setPaint(Color.BLACK); g2d.fillRect(0, 0, getSize().width, getSize().height); //print some status information g2d.setColor(Color.WHITE); g2d.drawString("Ship: " + Math.round(ship.getX()) + "," + Math.round(ship.getY()) , 5, 10); g2d.drawString("Move angle: " + Math.round( ship.getMoveAngle())+90, 5, 25); g2d.drawString("Face angle: " + Math.round( ship.getFaceAngle()), 5, 40); //draw the game graphics drawShip(); drawBullets(); drawAsteroids(); //repaint the applet window paint(g); } /***************************************************** * drawShip called by applet update event *****************************************************/ public void drawShip() { // set the transform for the image ship.transform(); ship.draw(); //draw bounding rectangle around ship if (showBounds) { g2d.setTransform(identity); g2d.setColor(Color.BLUE); g2d.draw(ship.getBounds()); } } /***************************************************** * drawBullets called by applet update event *****************************************************/ public void drawBullets() { for (int n = 0; n < BULLETS; n++) { if (bullet[n].isAlive()) { //draw the bullet g2d.setTransform(identity); g2d.translate(bullet[n].getX(), bullet[n].getY()); g2d.setColor(Color.MAGENTA); g2d.draw(bullet[n].getShape()); } } } /***************************************************** * drawAsteroids called by applet update event *****************************************************/ public void drawAsteroids() { for (int n = 0; n < ASTEROIDS; n++) { if (ast[n].isAlive()) { //draw the asteroid g2d.setTransform(identity); g2d.translate(ast[n].getX(), ast[n].getY()); g2d.rotate(Math.toRadians(ast[n].getMoveAngle())); g2d.setColor(Color.DARK_GRAY); g2d.fill(ast[n].getShape()); //draw bounding rectangle if (showBounds) { g2d.setTransform(identity); g2d.setColor(Color.BLUE); g2d.draw(ast[n].getBounds()); } } } } /***************************************************** * applet window repaint event--draw the back buffer *****************************************************/ public void paint(Graphics g) { g.drawImage(backbuffer, 0, 0, this); } /***************************************************** * thread start event - start the game loop running *****************************************************/ public void start() { gameloop = new Thread(this); gameloop.start(); } /***************************************************** * thread run event (game loop) *****************************************************/ public void run() { //acquire the current thread Thread t = Thread.currentThread(); //keep going as long as the thread is alive while (t == gameloop) { try { Thread.sleep(20); } catch(InterruptedException e) { e.printStackTrace(); } //update the game loop gameUpdate(); repaint(); } } /***************************************************** * thread stop event *****************************************************/ public void stop() { gameloop = null; } /***************************************************** * move and animate the objects in the game *****************************************************/ private void gameUpdate() { updateShip(); updateBullets(); updateAsteroids(); checkCollisions(); } /***************************************************** * Update the ship position based on velocity *****************************************************/ public void updateShip() { //update ship's X position, wrap around left/right ship.incX(ship.getVelX()); if (ship.getX() < -10) ship.setX(getSize().width + 10); else if (ship.getX() > getSize().width + 10) ship.setX(-10); //update ship's Y position, wrap around top/bottom ship.incY(ship.getVelY()); if (ship.getY() < -10) ship.setY(getSize().height + 10); else if (ship.getY() > getSize().height + 10) ship.setY(-10); } /***************************************************** * Update the bullets based on velocity *****************************************************/ public void updateBullets() { //move the bullets for (int n = 0; n < BULLETS; n++) { if (bullet[n].isAlive()) { //update bullet's x position bullet[n].incX(bullet[n].getVelX()); //bullet disappears at left/right edge if (bullet[n].getX() < 0 || bullet[n].getX() > getSize().width) { bullet[n].setAlive(false); } //update bullet's y position bullet[n].incY(bullet[n].getVelY()); //bullet disappears at top/bottom edge if (bullet[n].getY() < 0 || bullet[n].getY() > getSize().height) { bullet[n].setAlive(false); } } } } /***************************************************** * Update the asteroids based on velocity *****************************************************/ public void updateAsteroids() { //move and rotate the asteroids for (int n = 0; n < ASTEROIDS; n++) { if (ast[n].isAlive()) { //update the asteroid's X value ast[n].incX(ast[n].getVelX()); if (ast[n].getX() < -20) ast[n].setX(getSize().width + 20); else if (ast[n].getX() > getSize().width + 20) ast[n].setX(-20); //update the asteroid's Y value ast[n].incY(ast[n].getVelY()); if (ast[n].getY() < -20) ast[n].setY(getSize().height + 20); else if (ast[n].getY() > getSize().height + 20) ast[n].setY(-20); //update the asteroid's rotation ast[n].incMoveAngle(ast[n].getRotationVelocity()); if (ast[n].getMoveAngle() < 0) ast[n].setMoveAngle(360 - ast[n].getRotationVelocity()); else if (ast[n].getMoveAngle() > 360) ast[n].setMoveAngle(ast[n].getRotationVelocity()); } } } /***************************************************** * Test asteroids for collisions with ship or bullets *****************************************************/ public void checkCollisions() { //check for ship and bullet collisions with asteroids for (int m = 0; m<ASTEROIDS; m++) { if (ast[m].isAlive()) { //check for bullet collisions for (int n = 0; n < BULLETS; n++) { if (bullet[n].isAlive()) { //perform the collision test if (ast[m].getBounds().contains( bullet[n].getX(), bullet[n].getY())) { bullet[n].setAlive(false); ast[m].setAlive(false); continue; } } } //check for ship collision if (ast[m].getBounds().intersects(ship.getBounds())) { ast[m].setAlive(false); ship.setX(320); ship.setY(240); ship.setFaceAngle(0); ship.setVelX(0); ship.setVelY(0); continue; } } } } /***************************************************** * key listener events *****************************************************/ public void keyReleased(KeyEvent k) { } public void keyTyped(KeyEvent k) { } public void keyPressed(KeyEvent k) { int keyCode = k.getKeyCode(); switch (keyCode) { case KeyEvent.VK_LEFT: //left arrow rotates ship left 5 degrees ship.incFaceAngle(-5); if (ship.getFaceAngle() < 0) ship.setFaceAngle(360-5); break; case KeyEvent.VK_RIGHT: //right arrow rotates ship right 5 degrees ship.incFaceAngle(5); if (ship.getFaceAngle() > 360) ship.setFaceAngle(5); break; case KeyEvent.VK_UP: //up arrow adds thrust to ship (1/10 normal speed) ship.setMoveAngle(ship.getFaceAngle() - 90); ship.incVelX(calcAngleMoveX(ship.getMoveAngle()) * 0.1); ship.incVelY(calcAngleMoveY(ship.getMoveAngle()) * 0.1); //********* if (!thrust.getClip().isActive()) //**** thrust.play(); break; //Ctrl, Enter, or Space can be used to fire weapon case KeyEvent.VK_CONTROL: case KeyEvent.VK_ENTER: case KeyEvent.VK_SPACE: //fire a bullet currentBullet++; if (currentBullet > BULLETS - 1) currentBullet = 0; bullet[currentBullet].setAlive(true); //point bullet in same direction ship is facing bullet[currentBullet].setX(ship.getCenterX()); bullet[currentBullet].setY(ship.getCenterY()); bullet[currentBullet].setMoveAngle(ship.getFaceAngle() - 90); //fire bullet at angle of the ship double angle = bullet[currentBullet].getMoveAngle(); double svx = ship.getVelX(); double svy = ship.getVelY(); bullet[currentBullet].setVelX(svx + calcAngleMoveX(angle) * 2); bullet[currentBullet].setVelY(svy + calcAngleMoveY(angle) * 2); break; case KeyEvent.VK_B: //toggle bounding rectangles showBounds = !showBounds; break; } } /***************************************************** * calculate X movement value based on direction angle *****************************************************/ public double calcAngleMoveX(double angle) { double movex = Math.cos(angle * Math.PI / 180); return movex; } /***************************************************** * calculate Y movement value based on direction angle *****************************************************/ public double calcAngleMoveY(double angle) { double movey = Math.sin(angle * Math.PI / 180); return movey; } } </code></pre> <hr> <h2>ImageEntity.java</h2> <pre><code>/********************************************************* * Base game image class for bitmapped game entities **********************************************************/ import java.awt.*; import java.awt.Graphics2D; import java.awt.geom.*; import java.applet.*; import java.net.*; public class ImageEntity extends BaseGameEntity { //variables private Image image; private Applet applet; private AffineTransform at; private Graphics2D g2d; //default constructor ImageEntity(Applet a) { applet = a; setImage(null); setAlive(true); } //sets and returns the entity's image object public Image getImage() { return image; } public void setImage(Image image) { this.image = image; } //returns the width and height of the entity public int width() { return getImage().getWidth(applet); } public int height() { return getImage().getHeight(applet); } //returns the center of the entity in pixels public double getCenterX() { return getX() + width() / 2; } public double getCenterY() { return getY() + height() / 2; } //set reference to the drawing object public void setGraphics(Graphics2D g) { g2d = g; } private URL getURL(String filename) { URL url = null; try { url = this.getClass().getResource(filename); } catch (Exception e) { } return url; } //load an image file public void load(String filename) { setImage(applet.getImage(getURL(filename))); while(getImage().getWidth(applet) <= 0); double x = applet.getSize().width/2 - width()/2; double y = applet.getSize().height/2 - height()/2; at = AffineTransform.getTranslateInstance(x, y); } //move and rotate the entity public void transform() { at.setToIdentity(); at.translate((int)getX() + width()/2, (int)getY() + height()/2); at.rotate(Math.toRadians(getFaceAngle())); at.translate(-width()/2, -height()/2); } //draw the entity public void draw() { g2d.drawImage(getImage(), at, applet); } //bounding rectangle public Rectangle getBounds() { return new Rectangle((int)getX(),(int)getY(),width(),height()); } } </code></pre> <p>I understand that it seems as if the code can't find spaceship1.png, but I assure you it's there. Why would the code compile and work completely fine in AppletViewer, but then throw this exception only in the browsers?</p>
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<java><browser><applet><nullpointerexception><awt>
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Nullpointerexception in Browser but not AppletViewer
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