Should a utility class be static? [closed]

Question

If I have to design a Utility class( such as ByteUtils or StreamUtils or StringUtils), what is the best design choice for them.

• Should they be static classes (as I won't have any states to store)
• Should they be non-static classes ( so that if the objects are not used, they will be gc'd)

PS: By static class, I meant a class with static methods(and not the inner static class)

Please give advice on design choices for this ?

Answer 1

My utility classes look like this:

// final, because it's not supposed to be subclassed
public final class FooUtil {

    // private constructor to avoid unnecessary instantiation of the class
    private FooUtil() {
    }

    public static int doSomethingUseful() {
    }

    // ...
}

Note that, although this makes the utility methods easily testable, and easily accessible from the outside, it also makes the classes using them hard to unit-test, because it's not easy to mock these utility methods. Having too many of such utility classes can be a sign of a lack of OO design (procedural programming), and can really make the code hard to test.

If you're using a dependency injection framework (Spring, Guice, whatever), it might be a good idea to just make the utility class instantiatable, with non-static methods, and make it an injectable singleton. This way, classes using these utility methods can be tested by mocking the utility object.

Answer 2

If it is a general purpose utility, static is IMO better. You stated that you will not have any states to store, so I don't see why should you make it non-static. Declaring it to be static will save memory too.

Answer 3

Just because something can be static, doesn't mean it should be static.

There is another consideration to all this: mocking. It's harder to mock static methods in your tests than it is to mock the behaviour of an instance of a class.

Talk of unnecessary heap allocations and GCing of objects smacks of premature optimisation to me. The JVM will do a pretty good job at optimising away this sort of issue.