public void addCollideWithGroup(int collisionGroup) {
        this.collisionGroupsMask = this.collisionGroupsMask | collisionGroup;
    }
Add a group that this object will collide with.<br>
Two object will collide when <b>one</b> of the parties has the
collisionGroup of the other in its collideWithGroups set.<br>

@param collisionGroup the groups to add, ORed together (bitmask)
jme3-jbullet/src/main/java/com/jme3/bullet/collision/PhysicsCollisionObject.java