In the Smalltalk language there is a nice feature - Classes and methods can have set a category. In Java classes are divided into packages, but there is lack of method categories.
Category has only a documenting meaning, it has no importance for building and running the application. You just say, that the method is, for example, initializing instances. And an other method can be marked as "converting" and anybody now knows, that the method is used to convert the object to any other type or via versa. Probably the most usual and useful usage of such as marking is generating javadoc - you can generate javadoc that would have methods divided into categories. Such a documentation would be generally more useful.
It would be useful, to have a set of common categories, that are well known by all developers. Developers can, of course, use their project specific categories (for example "CustomerSupport").
Probably the most natural way to add categories is to add a @category("name") anotation for method or add @category as a javadoc tag.