Just learn openGL. No point to learn useless technology that don't convert to actual knowledge.
These kind of posts aren't helpful at all... if the OP wants to use other means to an end, let him. To say there's no point, is to just deprive knowledge which may in fact become useful at some point.
Me personally, when I used to use Java2D, I would always choose the pixelArray route; I like to have control of everything
What first turned me onto the pixel array method was the speed increase. I used a simple Bitmap class I wrote which supported an additional array for alpha values, and so I essentially did all the graphical stuff myself.
It's hindsight from professional graphics programmer that played with java2d not so long ago and haven't done anything with that gained knowledge. It's simply useless.