1. float inc = 0;
   [...]
   void draw(){
         pushMatrix();
         rotateX(inc);
         // In an arrayList or in a basic 2d array, you put the inc value beside the frame count of the sketch
         // to get this value, try frameCount() function.
         box(10);
         popMatrix();
         inc += 0.01;
   }

Look at: http://processing.org/reference/frameCount.html

In the future, you may also be interested by : http://processing.org/reference/modelX_.html

good luck

instead...
maybe you need something like this :

1. pushMatrix();
2. // milliseconds as reference
3. rotateX(millis()/1000.);
4. // frameCount as reference
5. //rotateX(frameCount / 100.);
6. box(10);
7. popMatrix();

Ho sorry, by frame I didn't mean related to time... but to the global reference axis of the 3D univers where 3D objects are created.

It seems to do the same on my sketche.