Question

I’d like to be able to declare a Java class Ref such that I could, elsewhere in code, do things like this:

switch (v)
{
case Ref.LicenseCode:                     ....;
case Ref.Widget.MaxWeight:                ....;
case Ref.Widget.MolyBolt.ThreadsPerInch:  ....;
}

Ref is intended to be constant data structure representing a hierarchical set of constant values, such as often appears in standards documents or other reference material. I want values that are truly constant (so they can be used in a case statement).

I thought I might be able to do this by nesting class definitions, and it works… to a point. For example this:

public final class Ref
{
    public final static int LicenseCode = 800;

    public final class Widget
    {
        public final static int MaxWeight = 5000;
    }
}

lets me write this:

switch (v)
{
case Ref.LicenseCode:                     ....;
case Ref.Widget.MaxWeight:                ....;
}

but when I try to nest down to the third level:

public final class Ref
{
    public final static int LicenseCode = 800;

    public final class Widget
    {
        public final static int MaxWeight = 5000;

        public final class MolyBolt
        {
            public final static int ThreadsPerInch = 12;
        }
    }
}

I am told that:

"Ref.Widget.MolyBolt cannot be resolved or is not a field."

Am I doing something wrong? Or have I bumped up against one of the edges of Java? Is there some other way to accomplish my goal? I am running under Windows Vista, JCK 1.6.0-21, using Eclipse Java Development Tools 3.5.2.r352.

Answer 1

How are you referencing the ThreadsPerInch field? This works for me:

public final class Ref {
    public final static int LicenseCode = 800;
    public final class Widget {
        public final static int MaxWeight = 5000;
        public final class MolyBolt {
            public final static int ThreadsPerInch = 12;
        }
    }
    public static void main(String[] args) {
        int v = Integer.valueOf(args[0]);
        switch (v) {
            case Ref.LicenseCode:
                break;
            case Ref.Widget.MaxWeight:
                break;
            case Ref.Widget.MolyBolt.ThreadsPerInch:
                break;
        }
    }
}

The only thing I’d change is to make inner classes static, though you’re probably not going to instantiate any objects of this class anyway.