In bean-managed persistence, a primary key can be a serializable object defined specifically for the bean by the bean developer. The primary key defines attributes we can use to locate a specific bean in the database. For the ShipBean we need only one attribute, id, but in other cases a primary key may have several attributes, which together uniquely identify a bean’s data.

We will examine primary keys in detail in Chapter 10; for now, we specify that the Ship EJB uses a simple single-value primary key of type java.lang.Integer. The actual persistence field in the bean class is an Integer named id.