Advantage of Static class over use of Singleton

Question

Duplicate

What’s wrong with singleton?
Singletons: good design or a crutch?
Singleton: How should it be used
What is so bad about Singletons

---

You can find numerous reasons for using a Singleton over a Static class. But there must surely be some situations where it is better to use a static class before a Singleton. What are they?

Answer 1

A singleton is a class of which only one instance can be instantiated, whereas there is no instance associated with a static method.

If you can implement the function you want with a single static method, then that is probably your best approach, because it is easier to implement. Consider extension methods - they are just static methods with syntactic sugar. If you can logically view the static method as a helper to an existing class, then it makes sense to use a static method.

On the other hand, if there is some sort of state involved in the functionality you are trying to achieve, then it is probably best to use a Singleton instead. The Singleton object can contain/manage its state and manage concurrent access/threading, whereas this becomes much more complicated with static classes and static methods. If you are using Singleton's in C#, I highly recommend reading Jon Skeet's article on proper Singleton implementation, which is available at http://www.yoda.arachsys.com/csharp/singleton.html .

Singleton's are more comparable to static classes than static methods. A big advantage that singletons have in this comparison is that they can implement interfaces and derive from base classes. This allows you to decouple their implementations from their interfaces. For example, if I have an interface IAccountService in my core assembly with a Singleton implementation, SingletonAspNetAccountService in my service layer, then I can inject the IAccountService into my UI layer with an IoC container, without requiring a dependency on my service layer in the UI layer. On the other hand, if I had a static Accounts class, then I would have to either create an adapter to the static class's methods or have a dependency on the service layer in my UI in order to access the static account functionality.

Answer 2

You can use static class when:

1) all its methods are utilities (nice example - class Math)

2) you don't want to deal with preserving your instance from garbage collector (in applets), but I would better use singleton there

3) you are absolutely sure that it wouldn't become stateful in the future and you are sure that you will always need only one instance of that class

If you are using singleton and in one moment you realize that you need several instances then your singleton easily can be transformed to multitone, but you'll have a problem with static class

Answer 3

Having fought with the testability of consumers of static classes over the years I can honestly say that they are the work of evil minds. Seriously though, I'd use static classes for extention methods in C# but not really anywhere else.

Answer 4

If your class doesn't store any state, then use a Static class.

If it stores state and you require a single instance, then (maybe) use a Singleton.

Otherwise use a regular class.

Answer 5

Static class is better for when you don't need to change the implementation. With a Singleton, you can have an interface with various implementations. A Static class, can only be an implementation.

Answer 6

It's always where you don't actually need to pass the singleton instance anywhere. For example, singleton will be useful if it implements some interface, you can't do it with a static class.

Remember, every Class instance is a singleton, managed by JVM. So static class is a singleton.