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Singleton: How should it be used
hello. i want to know what a singleton is? how to use it? and why do i have to use it. thank you very much. if anybody can give examples with the explanation i would really appreciate it.
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jose gabriel
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2http://en.wikipedia.org/wiki/Singleton_pattern – badgerr Jan 25 '11 at 15:14
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http://stackoverflow.com/questions/815528/how-to-answer-the-interview-question-what-is-a-singleton-and-how-would-you-use – Sebastian Paaske Tørholm Jan 25 '11 at 15:16
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1Congratulations, you made a step in the right direction by asking "why". – Jan 25 '11 at 15:17
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http://www.devarticles.com/c/a/Cplusplus/C-plus-plus-In-Theory-The-Singleton-Pattern-Part-I/ – DumbCoder Jan 25 '11 at 15:18
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@jose: One word: DONT. Singletons are usually the wrong thing. A crutch for lazy programmers that brings with it many new problems. – John Dibling Jan 25 '11 at 15:26
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so if i dont use them. what can i do to be sure that only one instance of a class will be created??. – jose gabriel Jan 25 '11 at 17:05
1 Answers
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If you need only a single instance of an object, then you use singleton. It is one of the many standard design patterns.
Let me clarify with a piece of code -
public class SingleInstance
{
private static final SingleInstance OnlyInstance = new SingleInstance(); // Or Any other value
// Private constructor, so instance cannot be created outside this class
private SingleInstance(){};
public static getSingleInstance()
{
return OnlyInstance;
}
}
Since this class's constructor is private, it cannot be instantiated in your application, thus ensuring that you have exactly one instance of class SingleInstance.
Use this pattern when you need to ensure only one instance of a particular class is created within your entire application.
To learn more, go here.
MD Sayem Ahmed
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2-1: NO. If you need only one instance of an object, then **freaking only instantiate it once**! Singletons are Bad for a number of reasons enumerated elsewhere. – John Dibling Jan 25 '11 at 15:25
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@John Dibling: Could you please provide the link? It would be a great help. – MD Sayem Ahmed Jan 25 '11 at 15:27
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@Sayem: Here's another link: http://stackoverflow.com/questions/86582/singleton-how-should-it-be-used – John Dibling Jan 25 '11 at 15:31
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