This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
An abstract class is a class that cannot be instantiated. An abstract method is a method that has no implementation. An abstract class need not have any abstract methods, but a class that has an abstract method must be declared an abstract class. Also, any class that subclasses an abstract class or interface and does not override all the methods must also be declared abstract.