Using interfaces for writing DAO classes

java data-access-layer data-access
Srini Kandula picture Srini Kandula · Dec 21, 2010 · Viewed 7.5k times · Source

I'm creating a new web application which will use a bunch of Data Access Object(DAO) classes for doing CRUD operations on the data. I know I should write java interfaces when I have external users/applications using my DAO classes. But if there is no such need do you think I should still write the interfaces? I'll be injecting DAO classes in to the Spring Controller(I'm using Spring MVC) classes using spring.

Answer

ColinD picture ColinD · Dec 21, 2010

Yes, you should. Your classes that use them should rely on the interfaces only. This enables you to easily initialize the client classes with fake implementations of your DAOs in order to test those classes, among other things. If you just use a concrete class, then the clients of your DAOs will depend directly on that single (database accessing) implementation and be very difficult to test.

The ease of making classes rely only on interfaces for services they depend on is one of the main strengths of dependency injection and you'd be doing yourself and your application a disservice by not taking advantage of it.

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