With CMP in EJB2.0 you'll only have to define the fields in your entity bean through the deployment descriptor. In your entity bean class you only got your getter/setter methods and no fields. These fields are defined through the methods and are called virtual fields.
Hence your methods are all abstract in the bean class, the container will override them, providing all necessary actions to you. This is also called implicit middleware...
But I would suggest, that you read a good book on EJBs like EJB Design
Patterns: Advanced Patterns, Processes, and Idioms by Floyd Marinescu
Have fun,
Ralf