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In a language that supports inheritance, an abstract class, or abstract base class (ABC), is a class that cannot be directly instantiated. By contrast, a concrete class is a class that can be directly instantiated. Instantiation of an abstract class can occur only indirectly, via a concrete subclass.
In class-based object-oriented programming, abstract types are implemented as abstract classes (also known as abstract base classes), and concrete types as concrete classes. In generic programming , the analogous notion is a concept , which similarly specifies syntax and semantics, but does not require a subtype relationship: two unrelated ...
In class-based programming, the most popular style, each object is required to be an instance of a particular class. The class defines the data format or type (including member variables and their types) and available procedures (class methods or member functions) for a given type or class of object.
Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should favor polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) over inheritance from a base or parent class. [2]
In software engineering and programming language theory, the abstraction principle (or the principle of abstraction) is a basic dictum that aims to reduce duplication of information in a program (usually with emphasis on code duplication) whenever practical by making use of abstractions provided by the programming language or software libraries. [1]
Decorator UML class diagram. The decorator pattern can be used to extend (decorate) the functionality of a certain object statically, or in some cases at run-time, independently of other instances of the same class, provided some groundwork is done at design time.
This makes it possible to change the implementation without affecting the clients. If the implementation is exposed, it is known instead as a transparent data type. Modern object-oriented languages, such as C++ and Java, support a form of abstract data types. When a class is used as a type, it is an abstract type that refers to a hidden ...
Later, HTML was reformulated (version 2.0) to be more of an SGML application; however, the HTML markup language has many legacy- and exception-handling features that differ from SGML's requirements. HTML 4 is an SGML application that fully conforms to ISO 8879 – SGML. [14]