protected void preRebuild() {
        collisionShape.calculateLocalInertia(mass, localInertia);
        if (constructionInfo == null) {
            constructionInfo = new RigidBodyConstructionInfo(mass, motionState, collisionShape.getCShape(), localInertia);
        } else {
            constructionInfo.mass = mass;
            constructionInfo.collisionShape = collisionShape.getCShape();
            constructionInfo.motionState = motionState;
        }
    }
Builds/rebuilds the physics body when parameters have changed
jme3-jbullet/src/main/java/com/jme3/bullet/objects/PhysicsRigidBody.java