I have been messing around with the ControlP5 library and noticed that the library manages to redraw objects (say, a slider bar or toggle box) without explicitly calling a draw() method for the object.

All examples I can find on the processing site seem to take this (or similar) approach (pseudo-code):

void draw() {
 a.draw();
 b.update();
}

But the ControlP5 library somehow updates objects (such as changing the color of a box from a mouseover) without explicitly calling a 'draw()' or 'update()' method.

My question is: Is there a way to incorporate 'automatic' updating somehow so each object doesn't have to be explicitly called? Could this be done with a listener? If so, could an 'event' be triggered for a mouseover?

Thanks in advance!

Yes it is, the function is "registerDraw(myObject)" and that will call a draw(); function of the object you pass every frame.