I have had the opportunity to interview several Java developers who claim to have 5+ years of development experience, yet they fail to answer this simple question. This tells me one thing: You are not learning your profession.

What is an abstract class?

An abstract class is a class marked abstract, it may include abstract methods. Abstract classes can not be instantiated, but can be subclassed. Abstract classes provide a partial implementation, leaving it to subclasses to provide the complete implementation.