FlxBox2D is a wrapper for Box2D through libgdx. The Box2D is a full JNI wrapper which means there's no garabage collection issues at all and the JNI call overhead is minimal.
JBox2D is a close Java port of Erin Catto's excellent C++ Box2D physics engine and Google's LiquidFun physics Engine.
Chipmunk2D is the official physics engine of Cocos2d, featuring full.
Real-time physics simulation.
A 2D Physics Engine for Games.