If I'm going to try and port Deskblocks to Java then I'll need to find a native Java physics API. If my only choices are native libraries then it makes more sense just to stick to Qt 4 - I'd rather keep this entirely in the "compile once run anywhere domain." Managing native libraries with wrappers functions is just a pain in the butt.
I was surprised to see slim pickins for physics API. For 2D physics I just found Phys2D and for 3D physics I found JBullet, a port of the Bullet physics API. Both seem to be great projects, and both seem to be currently active. Indeed, I'll probably give Phys2D a try and see if I can use it. I guess I just expected an ODE port by now.