Abstract and Final Methods and Classes

Using the ABSTRACT and FINAL additions of the METHODS and CLASS statements, you can define abstract and final methods or classes.

Abstract methods are declared in abstract classes and cannot be implemented in the same class but only in a subclass of the inheritance tree. Abstract classes can consequently not be instantiated. A non-abstract method is a concrete method. Except for the instance constructor, the concrete instance methods of a class can also call its abstract methods.

Final methods cannot be redefined in subclasses. Final classes cannot have any more subclasses and constitute the final node of an inheritance tree.

Note

In classes that are abstract and final at the same time, only the static components can be used. Instance components can be declared, but these cannot be used. For this reason, it is recommended that you specify both ABSTRACT and FINAL only for static classes.