Subclasses

Subclasses are a fundamental concept in object-oriented programming. A subclass is a class that is derived from another class, called the superclass. It inherits the superclass’s fields and methods and can add new ones or modify existing behavior through method overriding. Subclasses enable polymorphism, allowing code to interact with objects through a common base type while the actual object may be of a more specialized subclass.

Inheritance can follow different models. Many languages support single inheritance (one superclass) or multiple inheritance (several superclasses). Subclasses may be abstract, providing common behavior without being instantiated, or concrete, ready for use. They often rely on constructors that call the superclass constructor to ensure proper initialization. Overriding methods lets a subclass tailor or extend functionality, while still adhering to the expected interface of the base class. Languages differ in details, such as how to invoke base methods (for example, super() in Python or base:: in C++).

Design considerations include the benefits of reuse and extensibility versus potential downsides like tight coupling or the fragile base class problem. The Liskov Substitution Principle advises that objects of a subclass should be usable wherever the base class is expected. When to use inheritance versus composition is a common design decision; many practitioners favor composition to reduce fragility and increase flexibility.

In biology, the term subclass is also used as a taxonomic rank, positioned between class and order. It groups organisms within a class that share specific features, though the exact rank and its usage vary across classification systems. Thus, subclasses appear in both computing and biology as a means of organizing complexity through specialization.