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

1. Interfaces for one are contracts as I see them . For example , a set of software engineers(Implementation classes) may have a specific contract with a company(Interface) . The company may choose to switch between the engineers from time to time based on the project needs . Since they come under the same contract and follow the same rules , switching is easier than bringing in a resource from outside (writing a new class) every time the project needs change . You just have to change the configurations to switch the implementation classes .

2. Interfaces are clean and is a one point access to the rules which the classes implement .

Links

1. spring and interfaces
2. What does it mean to "program to an interface"?
3. http://www.artima.com/lejava/articles/designprinciples.html