Null Pointer Exception!

[Eric Ma]

Hi!
I run my game in J2ME Wireless ToolKit 2.2 successfully, but when I run my game in Nokia Mobile Internet Toolkit or a real nokia phone that had a error of Null Pointer Exception. The error was happened when some action changes in the game or exiting the game. Here is my program:

SpeedMIDlet.java

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class SpeedMIDlet extends MIDlet implements CommandListener {
private HCanvas canvas;
protected Image background;

public void startApp() {
if (canvas == null) {
canvas = new HCanvas(Display.getDisplay(this));
Command exitCommand = new Command("Exit", Command.EXIT, 0);
canvas.addCommand(exitCommand);
canvas.setCommandListener(this);
}

// Start up the canvas
canvas.start();
}

public void pauseApp() {}

public void destroyApp(boolean unconditional) {
canvas.stop();
}

public void commandAction(Command c, Displayable s) {
if (c.getCommandType() == Command.EXIT) {
destroyApp(true);
notifyDestroyed();
}
}
}

Some parts of HCanvas.java

public HCanvas(Display d) {
super(true);
display = d;

// Set the frame rate (30 fps)
frameDelay = 33;

// Clear the input delay
inputDelay = 0;
}

public void start() {
// Set the canvas as the current screen
display.setCurrent(this);

// Initialize the random number generator
rand = new Random();

// Initialize the game variables
gameOver = false;
numLives = 3;
score = 0;

// Initialize the background image and chicken and car sprites
try {
background = Image.createImage("/Highway.png");
chickenHead = Image.createImage("/ChickenHead.png");
speed = Image.createImage("/speed.png");

blackholeSprite[0] = new Sprite(Image.createImage("/Blackhole.png"));
blackholeSprite[0].setPosition(70, 77);
blackholeSprite[1] = new Sprite(Image.createImage("/Blackhole.png"));
blackholeSprite[1].setPosition(90, 107);
blackholeSprite[2] = new Sprite(Image.createImage("/Blackhole.png"));
blackholeSprite[2].setPosition(121, 60);
blackholeSprite[3] = new Sprite(Image.createImage("/Blackhole.png"));
blackholeSprite[3].setPosition(100, 20);

chickenSprite = new Sprite(Image.createImage("/Person.png"), 20, 26);
chickenSprite.setPosition(2, 77);

carSprite[0] = new Sprite(Image.createImage("/Car1.png"));
carSprite[0].setPosition(40, 0);
carYSpeed[0] = 4;
carSprite[1] = new Sprite(Image.createImage("/Car3.png"));
carSprite[1].setPosition(111, 67);
carYSpeed[1] = -4;

}
catch (IOException e) {
System.err.println("Failed loading images!");
e.printStackTrace();
}

// Initialize the music and wave players
try {
InputStream is = getClass().getResourceAsStream("Music.mid");
musicPlayer = Manager.createPlayer(is, "audio/midi");
musicPlayer.prefetch();
is = getClass().getResourceAsStream("Celebrate.wav");
celebratePlayer = Manager.createPlayer(is, "audio/X-wav");
celebratePlayer.prefetch();
is = getClass().getResourceAsStream("Squish.wav");
squishPlayer = Manager.createPlayer(is, "audio/X-wav");
squishPlayer.prefetch();
is = getClass().getResourceAsStream("GameOver.wav");
gameoverPlayer = Manager.createPlayer(is, "audio/X-wav");
gameoverPlayer.prefetch();
}
catch (IOException ioe) {
ioe.printStackTrace();
}
catch (MediaException me) {
me.printStackTrace();
}

// Start playing the music indefinitely
try {
musicPlayer.setLoopCount(-1);
musicPlayer.start();
}
catch (MediaException me) {
me.printStackTrace();
}

// Start the animation thread
sleeping = false;
Thread t = new Thread(this);
t.start();
}

public void stop() {
// Close the music and wave players
musicPlayer.close();
celebratePlayer.close();
squishPlayer.close();
gameoverPlayer.close();

// Stop the animation
sleeping = true;
}

public void run() {
Graphics g = getGraphics();

// The main game loop
while (!sleeping) {
update();
draw(g);
try {
Thread.sleep(frameDelay);
}
catch (InterruptedException ie) {ie.printStackTrace();}
}
}

private void update() {
// Check to see whether the game is being restarted
if (gameOver) {
int keyState = getKeyStates();
if ((keyState & FIRE_PRESSED) != 0) {
// Start a new game
try {
musicPlayer.setMediaTime(0);
musicPlayer.start();
}
catch (MediaException me) {
me.printStackTrace();
}
chickenSprite.setPosition(2, 77);
gameOver = false;
score = 0;
numLives = 3;
}

// The game is over, so don't update anything
return;
}

// Process user input to move the chicken
if (++inputDelay > 2) {
int keyState = getKeyStates();
if ((keyState & LEFT_PRESSED) != 0) {
chickenSprite.move(-6, 0);
chickenSprite.nextFrame();
}
else if ((keyState & RIGHT_PRESSED) != 0) {
chickenSprite.move(6, 0);
chickenSprite.nextFrame();
}
if ((keyState & UP_PRESSED) != 0) {
chickenSprite.move(0, -6);
chickenSprite.nextFrame();
}
else if ((keyState & DOWN_PRESSED) != 0) {
chickenSprite.move(0, 6);
chickenSprite.nextFrame();
}
checkBounds(chickenSprite, false);

// Reset the input delay
inputDelay = 0;
}

// See whether the chicken made it across
if (chickenSprite.getX() > 154) {
// Play a sound for making it safely across
try {
celebratePlayer.start();
}
catch (MediaException me) {
me.printStackTrace();
}

// Reset the chicken position and increment the score
chickenSprite.setPosition(2, 77);
score += 25;
}

// Update the car sprites
for (int i = 0; i < 2; i++) {
// Move the car sprites
carSprite[i].move(0, carYSpeed[i]);
checkBounds(carSprite[i], true);

for (int j = 0; j < 4; j++) {
// Move the blackhole sprites
blackholeSprite[j].move(0, 0);
checkBounds(blackholeSprite[j], true);

// Check for a collision between the chicken and cars
if ((chickenSprite.collidesWith(carSprite[i], true))||(chickenSprite.collidesWith(blackholeSprite[j], true))) {
// Play a sound for losing a chicken
try {
squishPlayer.start();
}
catch (MediaException me) {
me.printStackTrace();
}

// Check for a game over
if (--numLives == 0) {
// Stop the music and play a game over sound
try {
musicPlayer.stop();
gameoverPlayer.start();
}
catch (MediaException me) {
me.printStackTrace();
}

gameOver = true;
} else {
// Reset the chicken position
chickenSprite.setPosition(2, 77);
}

// No need to continue updating the car sprites
break;
}
}
}
}

Could anyone help me? Thx!

[balagopalks]

Have you tried in a Nokia emulator ? In which device are you trying? Please try to locate where you are getting the exception. Since there is no full code, I could not even compile and test the app.

Regards
Gopal

[soku123]

Hi,
Please tell which phone you are using......also just asking whether your images are properly displayed or some exceptions are occuring at that point.
Thanks
Soku

[Thygrrr]

Most likely the first call to paint(...) happens before all the images or resources are loaded. Make sure paint returns unless all data is present.

[Eric Ma]

I use Nokia Series 40 and Nokia 6230 phone for testing my game. But the result are the same. My game is downloaded into my 6230 phone successfully. And the images can be displayed on the screen. But the problem is Null Pointer Exception when my object is knocked down by car or obstacle and exiting the game. Thx!

[soku123]

can you point out where the exception occurs in the code...

Thanks
Soku

[Eric Ma]

Sorry! I can't point out where is the problem. I just see "Application error". and click in detail that show Null Pointer Exception - java/lang/NullPointerException

[soku123]

Hi,
Can u please explain the procedure for getting the exception.like playing the game and so on...If so we can figure it out.when will it come...

Thanks
Soku

[wang_shui]

Hi eric,

It may be due to the players used in ur game. Can u please give it a try by commenting all the audio players used in the application.


Wang

[balagopalks]

If you still have trouble, and if you dont have security issues with your code, please post your complete code/upload files in some server, so that some one could do some
round of debugging.

Regards
Gopal

[MananW]

Back to Basics.

Just Check have you specified correct names of images while craeting the images like in statement

new Sprite(Image.createImage("/Blackhole.png"));

As image names are case sensitive while running in the phone where as they run on the emulator.

[tzurs]

I agree with Wang,
I believe the problem is with the wave players. As far as my knowledge goes S40 phones (as 6230) are not able to create a player with content type wav.
If anyone was able to create a player for wav on a 6230 I would love to hear about it,
The null exception you get is thus on the player.

--tzurs

[sureshpathak2009]

Hi,
I want to play a song through midlet with .mp3 extension.
I have placed the song at "D:\hindi\classic\AA CHAL KE.MP3".
I want to access it through
p1=Manager.createPlayer(getClass().getResourceAsStream(
"\04 MUNGDA HO MUNGDA.mp3"), "audio/mpeg").
I mean iwant to know wheter is it right to given path is right or i have to write the full path or what else.
I am getting javanullpointer exception error.
So please guide me.
Thanks in advance...

[arpit2agrawal]

getResourceAsStream is used for reading files inside the jar file
If you want to access files outside jar file then you will have to use JSR 75 FileConnection API with path as "file:///D:/hindi/classic/AA CHAL KE.MP3"
Now don't waste your time in trying
getResourceAsStream("file:///D:/hindi/classic/AA CHAL KE.MP3")
It won't work...
Download and read JSR 75 - PIM and FC

[orenspor]

Could be that the format of the PNG for some reason cause the exception, on createImage(...) API.

Try use different format of the images.