Requirements for Entity Classes

An entity class must follow these requirements:

• The class must be annotated with the javax.persistence.Entity annotation.

• The class must have a public or protected, no-argument constructor. The class may have other constructors.

• The class must not be declared final. No methods or persistent instance variables must be declared final.

• If an entity instance is passed by value as a detached object, such as through a session bean’s remote business interface, the class must implement the Serializable interface.

• Entities may extend both entity and non-entity classes, and non-entity classes may extend entity classes.

• Persistent instance variables must be declared private, protected, or package-private, and can only be accessed directly by the entity class’s methods. Clients must access the entity’s state through accessor or business methods.