CSC/ECE 517 Fall 2012/ch2b 2w53 iv
Singleton, directory of sites
Singleton, directory of sites Pattern
1. http://en.wikipedia.org/wiki/Singleton_pattern
Topics Covered : Common uses, UML, Implementation, Example, Prototype based singleton, Example of use with factory method pattern
Summary : This link firstly provides the basic definition of the singleton pattern as a design pattern that restricts the instantiation of a class to one object. Singleton patters are mostly used in Abstract Factory, Builder, and Prototype, and Facade patterns.
Both the UML representation of singleton where the same single instance is always returned and the implementation concerning the mechanism to access the singleton class member without creating a class object and a mechanism to persist the value of class members among the class objects. The link also points out that if a class has to realize a contract expressed by an interface, it really has to be a singleton.
Lazy initialization uses double-checking and eager initialization which always creates an instance. It also talks about Prototype-based programming in which objects but not classes are used, a 'singleton' simply refers to an object without copies or that is not used as the prototype for any other object. Eg :-> Foo := Object clone ; Foo clone := Foo
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