Just Java™ 2

More Complicated Enumerated Types

Since enums are effectively classes, you can do pretty much everything with them that you can do with a class. In particular, you can provide one or more constructors for an enum type! That may seem a little weird to you (it does to me), because you never call an enum constructor anywhere in your code, or use the “new” operator to instantiate an enum. The definition of an enum brings the class enum constants into existence. You always work with static fields of an enum, not instances.

You might want to write a constructor when you have enumerations with a close relationship to numeric values. An example is an enumeration of hens' egg sizes, shown in Table 6-1. In the U.S., these are the names and weights ...