Interface Constants vs Class Constants variables

Question

I'm wondering what would be most likely to be use, Is it interface Constants or class Constants?

I have a code that has an interface like this:

public interface IConstantsVariableSupport {
     public String URL = "www.sample-me.com";
     public Integer LIMIT = 50;
}

This interface will support all the class that required its property constants. And I think that I can do it in a class also with constants in it like this:

public class ConstantsVariableSupport {
     public final static String URL = "www.sample-me.com";
     public final static Integer LIMIT = 50;
}

So my question is, What is the approach I will consider when using to support other classes with the constants they have. Is it using interface or a class? Or if likely, Can you suggest a best practice to handle a constant values for ease of use in the entire program. FYI I know how to use that two approaches, im just wondering how to do it right.

One perk of using an interface is that variables are *implicitly* `public static final`, so it doesn't have to be as verbose. — shmosel, Dec 06 '16 at 07:55
Another benefit of an interface is that a class can implement an interface and still inherit another class or interface. This was a popular hack to avoid declaring the class before [static imports](https://docs.oracle.com/javase/1.5.0/docs/guide/language/static-import.html) were introduced. — shmosel, Dec 06 '16 at 07:57

score 5 · Accepted Answer · answered Dec 06 '16 at 08:01

First, never create a single class or interface for dumping all of your constants. I know it is tempting but after 1 or 2 years, that constant file will become very messy and unreadable. Instead, if a variable has a very close relationship with a class, it is better to put the constant variable in that class. Here is what Joshua Bloch advises :

If the constants are strongly tied to an existing class or interface, you should add them to the class or interface. For example, all of the boxed numerical primitive classes, such as Integer and Double, export MIN_VALUE and MAX_VALUE constants. If the constants are best viewed as members of an enumerated type, you should export them with an enum type. Otherwise, you should export the constants with a noninstantiable utility class.

score 0 · Answer 2 · answered Dec 06 '16 at 07:59

0

I've always favoured option #2 - putting constants in a class. Option #1 can potentially save you some typing, since you don't need to explicitly indicate that your class variables are public static final (it's implied). However, think about what an interface actually is - it defines how you would interact with an object. Therefore, it's purpose is focused on behaviour.

answered Dec 06 '16 at 07:59

Riaan Nel

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Actually it doesn't matter. Either of them are not intended to be just a constants container, think what a class actually is: `A class is the blueprint from which individual objects are created`. – Diego Palomar Feb 14 '18 at 14:50

Interface Constants vs Class Constants variables

2 Answers2