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singleton
subject			fact

singleton	has definition A pattern that ensures that a certain class can have only one instance
	has context 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
	has example the Company or University classes in systems that run the business of that company or university
	has forces 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
	has problem How do you ensure that it is never possible to create more than one instance of a singleton class?
	has references one of the Gang of Four patterns.
	has solution 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
	is a subtopic of 6.5 - The Singleton Pattern
	is an instance of design pattern
design pattern	has antipatterns zero or more antipatterns - solutions that are inferior or do not work in this context with the reason for their rejection
	has name
	has related patterns zero or more related design patterns
	should be illustrated using a simple diagram
	should be written using a narrative writing style
pattern	should be as general as possible
	should be described in an easy-to-understand form so that people can determine when and how to use it
	should contain a solution that has been proven to effectively solve the problem in the indicated context

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