Disadvantages of using all static methods as opposed to other "service" classes?

Question

I have a simple Java application that carries out all its logic in the main method of one class.

Currently I have just created methods in this class, declared them as Static and called them in the main.

Is this approach preferred over e.g. creating a "service" class then creating an instance of it to invoke my methods?

a disadvantage: if one instance changes something for the method, it changes for all the calls made to it, since it is static — Stultuske, Mar 08 '16 at 10:37
you mean explain to you what static is? This is quite basic. Just lookup java static vs instance — Stultuske, Mar 08 '16 at 10:40

score 1 · Accepted Answer · answered Mar 08 '16 at 10:54

If your methods are puerly functional (no side-effects), then it's ok to use static methods. If they have side-effects (such as changing static class members), this design is dangerous as other parts of the system may suddenly break.

A more general problem is that its hard to unit-test such static methods, as they cannot easily be mocked. I this case it is preferrable to use a stingleton implementing an interface. This singleton can then be mocked by a "dummy"-implementation

see also this question on SO: Why aren't static methods considered good OO practice?

Disadvantages of using all static methods as opposed to other "service" classes?

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