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Java Data Objects by Craig Russell, David Jordan

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Changes Made by the Enhancer

The remainder of this chapter describes in more detail some of the changes made to your class files by the enhancer. We do not cover all the methods added by an enhancer. Nor do we explain all of the functionality added to a class to enable transparent persistence. You do not need to understand all the details of class enhancement; your application should never directly use the fields and methods added by enhancement. But it is useful, though not necessary, to have a basic understanding of how your classes are modified by the process. We list all the fields that are added by class enhancement and some of the methods. To gain a thorough understanding of the enhancement contract, you should read the JDO specification. You do not need to understand the remaining material in this chapter to use JDO. If you are not interested in the details of enhancement, you can skip over the remainder of this chapter.

The enhancer adds an interface, fields, and methods to your persistent classes so that they can be stored in a datastore transparently. The enhancer adds the following line to the definition of a persistent class:

implements javax.jdo.spi.PersistenceCapable

The PersistenceCapable interface defines methods the JDO implementation uses to manage instances in a JDO runtime environment. The enhancer adds the implementation of these PersistenceCapable methods. It also adds metadata information to each class, which is used by the JDO runtime environment to manage the ...

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