Question

I’m working on a custom particle system for a game I am beginning to work on. I have come upon a NullPointerException on my first test. I think I know why but I have no idea how I can fix it. Here is the related code:

ParticleSystem[] allParticles;

@Override
public boolean onTouchEvent(MotionEvent me){
    Random rand = new Random();
    allParticles[allParticles.length] = new ParticleSystem(
        rand.nextInt(10)+30,randomColor(),(int)me.getX(),(int)me.getY(), //this is 137
        rand.nextInt(10)+5,rand.nextInt(10)+5);
    return true;
}

Error:

08-04 20:53:27.579: ERROR/AndroidRuntime(16805): java.lang.NullPointerException
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at com.laytproducts.pixelinvaders.GamePanel.onTouchEvent(GamePanel.java:37)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.view.View.dispatchTouchEvent(View.java:3766)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:863)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:863)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:863)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1746)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1117)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.app.Activity.dispatchTouchEvent(Activity.java:2092)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1730)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1794)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.os.Looper.loop(Looper.java:143)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at android.app.ActivityThread.main(ActivityThread.java:4701)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at java.lang.reflect.Method.invokeNative(Native Method)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at java.lang.reflect.Method.invoke(Method.java:521)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
08-04 20:53:27.579: ERROR/AndroidRuntime(16805):     at dalvik.system.NativeStart.main(Native Method)

That probably really isn’t very good coding, so that’s why I need some help. I think it has something to do with the fact that I am using allParticles.length as the position to add the system, is there a better way to do this? I already tried turning it into an ArrayList then doing .add; it also gave me a NullPointerException which also makes me think it has something to do with the other part of line 137.

SOLVED

Did this:

@Override
public boolean onTouchEvent(MotionEvent me){
    Random rand = new Random();
    for(ParticleSystem p : allParticles){
        if(null == p){
            p = new ParticleSystem(rand.nextInt(10)+30,randomColor(),
                    (int)me.getX(),(int)me.getY(),15,15);
            Log.i("Pixel Invaders","ParticleSystem created: ");
            break;
        }
    }
    return true;
}

Answer 1

You have not initialized the allParticles array. And even if you initialize it,

allParticles=new ParticleSystem[10];

then still you cannot access allParticles[allParticles.length] element, since the array index is from 0 to allParticles.length-1.

So your code has two problems.