Why JPA Entity or Hibernate Persistence Class Should Not be Final?

One of the interesting hibernate interview questions is, why you should not make a Hibernate persistent class final? I'll try to answer this question in this short blog post. Use of proxies is the core feature of Hibernate (one of the most popular ORM framework for Java Projects) for implementing key performance features e.g. lazy loading and lazy associations fetching. In order to use a proxy in place of real class, your hibernate persistence class must be either non-final or the implementation of an interface that declares all of the public methods. Why? because you cannot extend a final class in Java, and to stand up as a proxy, proxy class must satisfy the IS-A relation, which comes either by extending a class using "extends", or implementing an interface using "implements".

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