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Singleton discussion
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I encountered some code at work that got me thinking.
There was a util - class that had some methods that had nothing to do with the state of the class. They were all "util" methods. Meaning that they could all be declared static with no problem because the only thing they did was some calculations and return the result.
But methods were declared non-static and the class was created as singleton. So even though an instance was needed to call them, because the class was singleton only one instance was created in the end.
I asked the programmer why the methods weren't declared static, and I was told that it is better to a have the class as singleton, than have the methods static.
I search the net for an answer:
http://forums.sun.com/thread.jspa?th...art=0&tstart=0
http://blogs.msdn.com/scottdensmore/...25/140827.aspx
http://www.ibm.com/developerworks/we...co-single.html
And the conclusion that i came is that it depends on the way you want to use the singleton class. Sometime it is better and sometimes you should avoid it depending on the implementation and how you want to use it.
Now I believe that the methods should be static in the case I described. What I would like, is a response about this comment:
Do you agree or not?
There was a util - class that had some methods that had nothing to do with the state of the class. They were all "util" methods. Meaning that they could all be declared static with no problem because the only thing they did was some calculations and return the result.
But methods were declared non-static and the class was created as singleton. So even though an instance was needed to call them, because the class was singleton only one instance was created in the end.
I asked the programmer why the methods weren't declared static, and I was told that it is better to a have the class as singleton, than have the methods static.
I search the net for an answer:
http://forums.sun.com/thread.jspa?th...art=0&tstart=0
http://blogs.msdn.com/scottdensmore/...25/140827.aspx
http://www.ibm.com/developerworks/we...co-single.html
And the conclusion that i came is that it depends on the way you want to use the singleton class. Sometime it is better and sometimes you should avoid it depending on the implementation and how you want to use it.
Now I believe that the methods should be static in the case I described. What I would like, is a response about this comment:
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I was told that it is better to a have the class as singleton, than have the methods static
Last edited by javaAddict; Oct 12th, 2009 at 5:35 am.
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#2 Oct 12th, 2009
It's common practice in the Java API to make "utility" methods static, so that makes it OK for me.
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#3 Oct 12th, 2009
static java methods is a bit slower than default methods .!
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#4 Oct 12th, 2009
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Originally Posted by msi_333 
static java methods is a bit slower than default methods .!
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#5 Oct 12th, 2009
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Originally Posted by msi_333
static java methods is a bit slower than default methods .!
Where did you get that information?
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#6 Oct 12th, 2009
I don't agree. let me give you the definition of static members and Singleton classes from a design point of view. static members are those that exist independent of every instances of that class. thus you would only use static members if they result to the same thing or same action for every instance of that class. Singleton objects exist because for every other object in the same context there should exist only one of it self.
I guess you already know this. its a programming flaw to to create a utility class and also make it possible to create instances of it. You should always prevent this by making its constructor private and provide no way of access an instance of such class (utility classes are only for convenience and should follow strict design rules).
If an instance is needed then it should not be a utility class
I guess you already know this. its a programming flaw to to create a utility class and also make it possible to create instances of it. You should always prevent this by making its constructor private and provide no way of access an instance of such class (utility classes are only for convenience and should follow strict design rules).
If an instance is needed then it should not be a utility class
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#7 Oct 12th, 2009
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Originally Posted by ejosiah
I don't agree. let me give you the definition of static members and Singleton classes from a design point of view. static members are those that exist independent of every instances of that class. thus you would only use static members if they result to the same thing or same action for every instance of that class. Singleton objects exist because for every other object in the same context there should exist only one of it self.
I guess you already know this. its a programming flaw to to create a utility class and also make it possible to create instances of it. You should always prevent this by making its constructor private and provide no way of access an instance of such class (utility classes are only for convenience and should follow strict design rules).
If an instance is needed then it should not be a utility class
Of course my concern was, is it better instead of having static methods to have a singleton class. In that way it will also be impossible to have many instances.
In one of the links I read, and I agree with it, was that you should not create your class to be as singleton, but if you want it to be initialized once then create a factory class with a method that will create and return only one instance.
In that way you don't limit others to use the class in any way they might see fit.
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#8 Oct 12th, 2009
creating a factory class just to instantiate a singleton object is redundant. factory classes are there to ease the creation of several classes not one. the best we to access a singleton object is via a factory method defined by the class itself i.e. getInstance. (see GOF design patterns for more info).
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#9 Oct 12th, 2009
I agree with you, addict. I found an interesting note on wikipedia as well: "Another notable difference is that static member classes cannot implement an interface, unless that interface is simply a marker. So if the class has to realize a contract expressed by an interface, it really has to be a singleton."
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#10 Oct 13th, 2009
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Originally Posted by ejosiah
creating a factory class just to instantiate a singleton object is redundant. factory classes are there to ease the creation of several classes not one
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Originally Posted by ejosiah
The best we to access a singleton object is via a factory method defined by the class itself i.e. getInstance. (see GOF design patterns for more info).
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