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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 ...
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.
override - Specifies that a method or property declaration is an override of a virtual member or an implementation of a member of an abstract class. readonly - Declares a field that can only be assigned values as part of the declaration or in a constructor in the same class.
In class-based programming, methods are defined within a class, and objects are instances of a given class. One of the most important capabilities that a method provides is method overriding - the same name (e.g., area) can be used for multiple different kinds of classes. This allows the sending objects to invoke behaviors and to delegate the ...
In object-oriented programming, a covariant return type of a method is one that can be replaced by a "narrower" (derived) type when the method is overridden in a subclass. A notable language in which this is a fairly common paradigm is C++. C# supports return type covariance as of version 9.0. [1]
This can require significantly less programming effort if the base class contains many methods providing default behavior and only a few of them need to be overridden within the derived class. For example, in the C# code below, the variables and methods of the Employee base class are inherited by the HourlyEmployee and SalariedEmployee derived ...
For instance, in C#, the base method or property can only be overridden in a subclass if it is marked with the virtual, abstract, or override modifier, while in programming languages such as Java, different methods can be called to override other methods. [15] An alternative to overriding is hiding the inherited code.
A couple of mainstream languages, Eiffel and Dart [9] allow the parameters of an overriding method to have a more specific type than the method in the superclass (parameter type covariance). Thus, the following Dart code would type check, with putAnimal overriding the method in the base class: