How can I determine when is more convenient to use static methods instead of instance ones? Encapsulation is the preferable choice?

Question

I am basically writing static methods that perform work on a list of strings but I can't quite determine if it would be better to create instance variable and do all the work internally. In case my question isn't clear: what needs to be accounted for when makes this decision? If encapsulation needs to be always the first choice, then I guess I would be better in choosing instance variables and methods.

Methods:

public static List<String> split(String string)
{
    List<String> list = new ArrayList<>();
    ...
    return list;
}

public static int count(List<String> stringBlocks)
{
    ...
    return counter;
}

private static List<String> createList(List<String> stringBlocks, int currentCap, int lastCap)
{
    List<String> list = new ArrayList<>();
    ...
    return list;
}
    
public static List<List<String>> makeJoinedLists(List<String> stringBlocks)
{
    List<List<String>> lists = new ArrayList<>();
    ...
    return lists;
}

public static List<String> performWork(List<List<String>> lists)
{
    List<List<String>> lists = new ArrayList<>();
    ...
    return lists;
}

stackoverflow.com/questions/2671496/when-to-use-static-methods I think this may be your answer :) — PastorPL
– PastorPL, Commented Mar 22, 2024 at 10:07
It’s not clear what advantage you expect from making these methods instance methods. If you can’t express the expected advantage, you should not make the change. Besides that, if you want an advice, do not use method names like “performWork”. — Holger
– Holger, Commented Mar 22, 2024 at 11:02

cyberbrain · Accepted Answer · 2024-03-22 11:47:42Z

What you are showing in your code is a Utility Class. It consists solely of static methods and has no own member fields. Ensure that you set its constructor to private, so that it cannot be instantiated by accident and you are fine.

But this does not have to do with encapsulation. Encapsulation means that you access the member fields of a class only via its methods. It does not mean that the methods of the class call other methods of other classes (static or not doesn't matter) with their own member fields as parameters. In fact I think that a program without such calls would not be useful.

What you should think about is testing: if you want to unit test the code that uses your utility class, it will be hard to test just the calling code without actually running the utility classes code as well (but then it's not a real unit test anymore). It is possible to have the static methods "mocked", but it is not very clean and hard to understand how that works so it could easily confuse a reader of the code and test.

So to design for testability you should not make those methods static, but regular methods of the object - so it will become easier to create a mock object of your class and use that in unit tests.

mufsalup · Accepted Answer · 2024-03-22 10:56:27Z

0

I found a similar question to yours here: When to use static methods

But I would also like to give you my opinion (because in the end it's your decision, as there won't be any significant performance issues for small and medium sized projects).

In your case, you want to add some features to the lists. Will this be a general solution (most likely described as UtilClass) for all lists or specifically for one list type. In the first case, you could also think about extending java.util.List or just use your static solution. In the second case, you should use your own type that extends java.util.List.

answered Mar 22, 2024 at 10:56

mufsalup

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