p. 188 EJB's 2nd Ed. by Monson-Haefel O'Reilly & Assoc. The no-augrument constructor is required for CMP. When a new bean is created, the container automatically instantiates the primary key using the Class.newInstance() method, and populates it from the class's container managed fields. A no aurgument constructor must exist in order for that to work.
With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.