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singleton comparison table

Subject	is a kind of	is a subtopic of	have example	is an instance of	have problem	have context	has definition	have solution	have forces	have references
design pattern	pattern	6.1 - Introduction to Patterns			a sentence or two explaining the main difficulty being tackled	a context	A pattern useful for the design of software		one or more forces	one or more references which indicate who developed or inspired a pattern
singleton		6.5 - The Singleton Pattern	the Company or University classes in systems that run the business of that company or university	design pattern	How do you ensure that it is never possible to create more than one instance of a singleton class?	In software systems, it is very common to find classes for which you want only one instance to exist. Such a class is called a singleton	A pattern that ensures that a certain class can have only one instance	In a singleton class, create the following: A private class variable, often called theInstance. This stores the single instance A public class method (static method) often called getInstance. The first time this method is called, it creates the single instance and stores it in theInstance. Subsequent calls simply return theInstance A private constructor, which ensures that no other class will be able to create an instance of the singleton class	If you use a public constructor, you cannot offer the guarantee that no more than one instance will be created The singleton instance must also be accessible to all classes that require it, so it must often be public	one of the Gang of Four patterns.

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