Abstract Classes in Java

Abstract classes are classes that contain one or more abstract methods. An abstract method is a method that is declared, but contains no implementation. Abstract classes may not be instantiated, and require subclasses to provide implementations for the abstract methods. Let's look at an example of an abstract class, and an abstract method.
When an operation is performed in a different way, it is a good candidate for an abstract method (forcing subclasses to provide a custom implementation).