Android : NullPointerException while adding Resources

I'm getting a NullPointerException when running this bit of code

abstract class thing extends Drawable(){
    Bitmap sprite;
    int spriteResource;

    public thing(){
          setResources();
          sprite=Bitmap.createBitmap(sprite,src.left,src.top,(src.right-src.left),(src.bottom-src.top),m,true);
    }

    @Override
    public void draw(Canvas c){
    bit= Bitmap.createBitmap(sprite,0,0,45,  45);// Generates the exception
    c.drawBitmap(bit, x, y, null);
    }

     abstract void setResource();
}

class otherThing extends thing(){
     @Override
      public void setResource(){
      spriteResource=R.drawable.otherThing_sprite;
      }开发者_C百科
}

Basically i'm trying to load different sprites into different classes by using the method of the parent class. But the spriteResource doesn't get set and I can't understand why? I set up the log which returned the Resource as 0. Any ideas why this is happening or how to resolve it???

Thanks

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When createBitmap in thing() is trying to give the sprite variable a value, sprite is one of its in-parameters, this means that you are trying to use sprite before it is created and you get a null pointer exception.