Class inheritance

Inheritance relates a derived class to a base class. A derived class can use inherited members and add its own, allowing shared behavior to be maintained together. Visibility and object construction follow language rules. Whether a hierarchy usefully represents a problem depends on the behavior of its objects as well as their names.

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A derived class may override an inherited method. Dynamic dispatch can select an implementation using the actual object type, allowing a common operation to produce type-specific behavior. Fields, static methods, and instance methods need not obey identical selection rules; matching names alone do not establish that every access is dynamically dispatched.

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Construction must initialize both base-class state and additions made by the derived class. Java constructors are not inherited as ordinary members, although a subclass constructor can invoke a superclass constructor. Python provides super for cooperative calls along its inheritance order. Initialization order and argument conventions must agree to produce a consistent object.

References: [1]

Python permits multiple base classes and defines a method resolution order; Java classes have one direct superclass, with separate interface rules. Shared ancestors require careful coordination. Composition offers another design: an object stores collaborators and delegates work to them. This expresses a use relationship without making every form of reuse part of a class hierarchy.

References: [2]