Suggest proper Design for Java integer constants extension

Question

I am sorry if this question was asked before, but I need a good suggestion to solve next design problem:

Task: given that we have a base service that operates with data of given set of types, we need to design support of extensions for that service that has extended type set.

Bad Solution:

class BaseServiceType {
    public static final int TYPE_A = 0;
    public static final int TYPE_B = 1;
    public static final int LAST_USED_BASE_TYPE_INDEX = TYPE_B;
}

And its extension

class ExtendedServiceType extends BaseServiceType {
   public static final int TYPE_E = LAST_USED_BASE_TYPE_INDEX + 1;
   public static final int TYPE_F = LAST_USED_BASE_TYPE_INDEX + 2;
}

My task is fairly simple that has only one extension. I am not trying to solve more general problem with multiple independent extensions.

I have a feeling that enum would work here, but no idea if it feasible.

Check [this discussion](http://stackoverflow.com/questions/1414755/java-extend-enum) about extending enums. I think it will be helpful for your situation. — , Dec 31 '13 at 11:05
Enums are immutable, you can not add new types during runtime. I don't know if I got your question right, but this might be a problem. If there are no new services added during runtime, you could use Enums — Mirco, Dec 31 '13 at 11:07
see http://stackoverflow.com/questions/1414755/java-extend-enum — Luigi R. Viggiano, Dec 31 '13 at 11:08
Thank you for a suggestion, but I doubt that introducing new type would not require additional wrapping to use those types — acm0x, Dec 31 '13 at 11:28

score 2 · Accepted Answer · answered Dec 31 '13 at 11:25

One solution is to build the ids dynamically. Class initilization is thread safe so you can do this.

class BaseServiceType {
    protected static int id = 0;
    public static final int TYPE_A = id++;
    public static final int TYPE_B = id++;
}

And its extension

class ExtendedServiceType extends BaseServiceType {
   public static final int TYPE_E = id++;
   public static final int TYPE_F = id++;
}


class AlsoExtendedServiceType extends BaseServiceType {
   public static final int TYPE_X = id++;
   public static final int TYPE_Y = id++;
}

The only problem is the order classes are initialized change the ids. If this matters, you need to access the classes in the order you need.

Great idea. I love it. Well, would it have more sense to use strings instead of ints? — acm0x, Dec 31 '13 at 11:35
@ACM64 You could, but I don't know how you would like to generate them automagically. ;) — Peter Lawrey, Dec 31 '13 at 12:00

Suggest proper Design for Java integer constants extension

1 Answers1