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Why not a class with static methods as replacement for Singleton object?

 
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Hi Experts,

I have seen this question asked in an interview.

Why we cannot use a class with static methods (and possibly with private constructor) as replacement for Singleton?

Please share your views.

regards,
Pushker chaubey
 
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Good question. My 2 cents is that in some cases a class with static methods would work out fine. But if you use an interface to describe the behavior of the singleton, you need an object to provide the implementation.
 
Pushker Chaubey
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Hi Max,

Thanks for a quick reply.


regards,
Pushker chaubey
 
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If your singleton class implements an interface or extends another class, then without the singleton instance you will not be able to use your class as a parameter or return value. A good example is String.CASE_INSENSITIVE_ORDER - a singleton Comparator<String> so you can use it in Collections.sort for instance. Another example is Collections.EMPTY_SET and its brothers - singleton Set, List etc implementations you can use as a return value if you have nothing to return:
This way, if you know that the complex steps are not necessary because you're going to return an empty Set anyway, you return the singleton which avoids the creation of a new object.
 
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If the class has static methods, why do you even need to care if the constructor is public or private?
 
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Maneesh Godbole wrote:If the class has static methods, why do you even need to care if the constructor is public or private?


Code clarity, you'de be presenting a way to users of your code to instantiate a class that has no non-static methods. Private constructors remove that option and as a result make developers use the class the way it was intended. That said I have a preference for the Singleton pattern even if an all static method class would do as well.
 
Pushker Chaubey
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Thanks guys!
 
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R van Vliet wrote:Code clarity, you'de be presenting a way to users of your code to instantiate a class that has no non-static methods. Private constructors remove that option and as a result make developers use the class the way it was intended



Note that this doesn't apply to abstract classes, since their subclasses may well include non-static methods.
 
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