Abstract Class

Abstract class is used to specify that a class is not to be instantiated, but rather inherited by other classes. An abstract class provides a base for someone to extend an actual class. An abstact class is deliberatesly missing some or all of the method bodies. An abstract class can have abstract methods that are not implemented in the abstract class, but in subclasses. You can't use new on abstract classes, but you can use abstract references, which always point to some extension of the abstract class. Unlike interfaces, abstract classes may implement some of the methods. Though you can't instantiate an abstract class, you can invoke its static methods.

Because an abstract class is not fully defined you cannot declare abstract constructors, or abstracr static methods. Any subclass of an abstract class must either implement all of the abstract methods in the superclas or be itself declared abstract.