Java - is it bad practice not to have a class constructor?

constructor, helper, java

Solution

Is it bad practice to leave out a constructor?

Yes - because unless you specify any constructors, the Java compiler will give you a constructor with the same visibility as the class itself.

Assuming all your methods are static - which seems likely unless you want polymorphism - you should make your class `final` and give it a `private` constructor, so that other developers don't accidentally create an instance of your class, when that would be pointless. When thinking about an API, any time I can remove the ability for developers to do something stupid, I do so :)

So something like:

public final class Helpers {
    private Helpers() {
    }

    public static String formatDate(Date date) {
        // etc
    }
}

Note that by taking polymorphism out of the equation, you're also removing the possibility of changing this behaviour for tests etc. That may well be fine - I'm not a believer in "no statics, ever" - but it's worth considering.

Problem

I want to make a helper class that deals with formatting (i.e. has methods to remove punctuation and convert between types, as well as reformatting names etc.). This doesn't seem like it will need any fields - its only purpose is to get passed things to convert and return them, reformatted. Is it bad practice to leave out a constructor? If so, what should my constructor be doing? I was looking at this link and noticed that the class it describes lacks a constructor.

Original source