3.2. The JDO Basics

The JDO specification defines 20 or so classes and interfaces in total, but a developer needs to know only five main classes (which are actually Java interfaces):

  • PersistenceManagerFactory

  • PersistenceManager

  • Extent

  • Query

  • Transaction

Figure 3-3 provides a simplified class diagram showing how these interfaces are related:

Figure 3-3. A simplified JDO class diagram.

A PersistenceManagerFactory is used to get a PersistenceManager instance. There is a one-to-many relationship between the PersistenceManagerFactory and the PersistenceManager. A PersistenceManagerFactory can create and manage many PersistenceManager instances and even ...

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