Java Data Objects

Lifecycle States

JDO has a total of 10 lifecycle states. The following 7 states are required:

• Transient

• Persistent-new

• Hollow

• Persistent-clean

• Persistent-dirty

• Persistent-deleted

• Persistent-new-deleted

There are also three optional states:

• Transient-clean

• Transient-dirty

• Persistent-nontransactional

If a JDO implementation does not support the transaction-related optional features that allow transient transactional and persistent-nontransactional instances, these three optional states are not reachable. This chapter focuses on the required states. Chapter 13 and Chapter 14 discuss these optional features and associated lifecycle states.

Transient

When you call a constructor to create an instance of a class, the instance is placed in the transient state. Each instance created by the application starts its life as a transient instance. Transient instances do not have a JDO identity, because identity is only a characteristic of persistent instances. A transient instance should behave exactly as an instance of the class would if the class were not persistent. No JDO exceptions are thrown for a transient instance.

Many developers wonder how much overhead is involved when transient instances of an enhanced class are manipulated. Fields of transient instances have slightly slower access and modification than they would if the class were not persistent and enhanced. No mediation of access or modification of fields is performed on instances in the transient state. In particular, a transient instance never ...