public void addCollisionGroupListener(PhysicsCollisionGroupListener listener, int collisionGroup) {
        collisionGroupListeners.put(collisionGroup, listener);
    }
Adds a listener for a specific collision group, such a listener can disable collisions when they happen.<br>
There can be only one listener per collision group.

@param listener the listener to register (not null, alias created)
@param collisionGroup which group it should listen for (bitmask with
exactly one bit set)
jme3-jbullet/src/main/java/com/jme3/bullet/PhysicsSpace.java