Defining Persistent Fields

In EJB 3.0, get and set methods are concrete, not abstract. In addition, these methods can include logic, something that was not possible previously. This is useful for actions such as validating fields. Another improvement is that access to the persistence fields is not limited to the get and set methods. The persistence fields are also accessible through a bean class's business methods. One restriction however is that in EJB 3.0 technology, only methods within the class can access persistence fields -- in other words, you cannot expose the instance variables outside of the class.

The EJB 2.0 specification lets you designate an entity bean’s instance variables as CMP fields or CMR fields. You define these fields in the deployment descriptor. CMP fields are marked with the element cmp-field, while container-managed relationship fields are marked with the element cmr-field.