what reasons are there to use interfaces (Java EE or Spring and JPA)

Question

Most of the J2EE(Spring and JPA) classes are designed with interfaces. Except for inheritance, are there any technical reasons for this? Like dynamic proxy

Answer 1

Because you have mentioned Spring explicite.

Spring AOP can be used in different configurations. The default one uses java dynamic proxies (java.lang.reflect.Proxy). This can be only applied to Interfaces

Spring AOP defaults to using standard J2SE dynamic proxies for AOP proxies. This enables any interface (or set of interfaces) to be proxied.

@see Spring Reference Chapter 7.1.3 AOP Proxies @see Dynamic Proxy Classes