An abstract class is a class that is partially implemented. It provides design convenience. An abstract class consists of one or more abstract methods that are declared but left unimplemented. It is the responsibility of subclasses that extend an abstract class to implement the unimplemented part of the abstract class. As the implementation of an abstract class is not complete, it is not possible to directly create objects of an abstract class.
A class containing one or more abstract methods must be declared as abstract. However, a class can also be declared as abstract even if it has no abstract methods. An abstract class may also have non-abstract methods.
Note: The final and abstract class modifiers are not used in combination.
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