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Due to the C++ language not having a dedicated keyword to declare interfaces, the following C++ example uses inheritance from a pure abstract base class. For most purposes, this is functionally equivalent to the interfaces provided in other languages, such as Java [4]: 87 and C#. [5]: 144
In C#, class methods, indexers, properties and events can all be overridden. Non-virtual or static methods cannot be overridden. The overridden base method must be virtual, abstract, or override. In addition to the modifiers that are used for method overriding, C# allows the hiding of an inherited property or method.
Multiple inheritance where one class can have more than one superclass and inherit features from all parent classes. "Multiple inheritance ... was widely supposed to be very difficult to implement efficiently. For example, in a summary of C++ in his book on Objective C, Brad Cox actually claimed that adding multiple inheritance to C++ was ...
The non-virtual interface pattern (NVI) controls how methods in a base class are overridden. Such methods may be called by clients and overridable methods with core functionality. [1] It is a pattern that is strongly related to the template method pattern. The NVI pattern recognizes the benefits of a non-abstract method invoking the subordinate ...
The curiously recurring template pattern (CRTP) is an idiom, originally in C++, in which a class X derives from a class template instantiation using X itself as a template argument. [1] More generally it is known as F-bound polymorphism , and it is a form of F -bounded quantification .
A notable language in which this is a fairly common paradigm is C++. C# supports return type covariance as of version 9.0. [1] Covariant return types have been (partially) allowed in the Java language since the release of JDK5.0, [2] so the following example wouldn't compile on a previous release:
The factory method design pattern solves problems such as: How can an object's subclasses redefine its subsequent and distinct implementation? The pattern involves creation of a factory method within the superclass that defers the object's creation to a subclass's factory method.
Also, derived classes can override inherited methods if the language allows. Not all languages support multiple inheritance. For example, Java allows a class to implement multiple interfaces, but only inherit from one class. [22] If multiple inheritance is allowed, the hierarchy is a directed acyclic graph (or DAG for short), otherwise it is a ...