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A design pattern is the re-usable form of a solution to a design problem. The idea was introduced by the architect Christopher Alexander [ 1 ] and has been adapted for various other disciplines, particularly software engineering .
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns. The book was written by Erich Gamma , Richard Helm , Ralph Johnson , and John Vlissides , with a foreword by Grady Booch .
A class diagram exemplifying the singleton pattern. In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance. It is one of the well-known "Gang of Four" design patterns, which describe how to solve recurring problems in object-oriented software. [1]
Efforts have also been made to codify design patterns in particular domains, including the use of existing design patterns as well as domain-specific design patterns. Examples include user interface design patterns, [ 7 ] information visualization , [ 8 ] secure design, [ 9 ] "secure usability", [ 10 ] Web design [ 11 ] and business model design.
In object-oriented programming, the factory method pattern is a design pattern that uses factory methods to deal with the problem of creating objects without having to specify their exact classes. Rather than by calling a constructor , this is accomplished by invoking a factory method to create an object.
The builder pattern is a design pattern that provides a flexible solution to various object creation problems in object-oriented programming.The builder pattern separates the construction of a complex object from its representation.
The observer design pattern is a behavioural pattern listed among the 23 well-known "Gang of Four" design patterns that address recurring design challenges in order to design flexible and reusable object-oriented software, yielding objects that are easier to implement, change, test and reuse.
A visitor pattern is a software design pattern that separates the algorithm from the object structure. Because of this separation, new operations can be added to existing object structures without modifying the structures.