A base class is a computer object that serves as the foundation for one or more derived classes, providing common functionality. It can be concrete or abstract and can have multiple subclasses. Different languages have different names and behaviors for base classes, but the principle remains the same.
A base class, also called a superclass, is a computer object that serves as the foundation for one or more derived classes. Any computer language capable of inheriting can create a base class. Depending on their precise type, base classes may or may not be able to initialize themselves, by assigning an initial value to an object, on their own, but they always give some kind of common functionality to any class that inherits from them. There is never a limit to the number of derived classes, or subclasses, that base classes can have, but there may be a limit, depending on the computer language, to the number of base classes a derived class can have. Languages that allow a derived class to have only one base are said to enforce single inheritance, while those that allow a derived class to have multiple base classes are said to use multiple inheritance.
Concrete base classes can be initialized by themselves; that is, an object of the base class type can be created. If an Example class is a basis for a derived class Example2, you can create an object of type Example2 and an object of type Example. An object of type Example can only be created by explicitly calling that type of object; creating an object of type Example2 does not create a child object of type Example. In each case, the type of object created creates only one instance of itself.
Abstract base classes, by contrast, cannot be initialized by themselves, which means that a base class object cannot be created by itself. If a class Example3 is an abstract base for a derived class Example4, only an object of type Example4 can be created. Even if type Example4 includes data of type Example3, attempting to create an object of type only Example3 will result in an error. This feature can be useful at times, particularly if the Example3 class contains private data that should be tightly regulated.
Depending on the language in which a base class appears, it can have slightly different behaviors and significantly different names. In Java® the base classes are always indicated with that name, while in C++, depending on their structure, they can be called virtual classes. The differences in name and functionality, while significant in terms of the computer languages used, do not imply major differences in the principle behind classes. A base class is always used to encapsulate common data and functionality for its derived classes, regardless of language.
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