In Java, how to iterate on the constants of an interface?

Question

in an interface, I store constants in this way (I\'d like to know what you think of this practice). This is just a dummy example.

interface HttpConstants {
    /         


        

Answer 1

I would create these constants as an enumeration. Enums in Java can have their own fields and methods, which very convenient for your case. So I would do this the following way:

enum HttpConstant {
    HTTP_OK(200),
    HTTP_CREATED(201),
    HTTP_ACCEPTED(202),
    HTTP_NOT_AUTHORITATIVE(203),
    HTTP_NO_CONTENT(204),
    HTTP_RESET(205),
    HTTP_PARTIAL(206);

    private final int id;

    HttpConstant(int id) {
        this.id = id;
    }

    int getId() {
        return id;
    }
}

Now the iteration is easy:

for (HttpConstant constant : HttpConstant.values()) {
    //Do something with the constant
}

This way it is also easy to add associate some new values with the constants, you just have to add new fields.

Right now you may use reflection:

Field[] interfaceFields = HttpConstants.class.getFields();
for (Field field : interfaceFields) {
    int constant = field.getInt(null);
    //Do something with the field
}

However, it is better to use the approach with enums because with reflection coding errors result in runtime exceptions instead of compile-time errors.