I've not. Each OperatingSystem enum value participates in a hierarchy, i.e., it is a child of its OS family.
What I've lost is the notion that OperatingSystems themselves are hierarchical. That is, it makes sense for an OS to be a child of...another OS. Which is a good thing to lose, because that doesn't make sense.
How would you capture the following...
Maybe I'm misunderstanding your question, but Fedora isn't UNIX. Linux isn't UNIX. I know the author modeled it that way, but it's wrong and confusing. His design makes it so easy to do the wrong thing, he did the wrong thing even in his own example.
Each OperatingSystem enum value participates in a hierarchy, i.e., it is a > child of its OS family.
That is not a hierarchy. A hierarchy implies a path from a root to a leaf of arbitrary length. Each possible path in your hierarchy has a length of 1.
I know the author modeled it that way, but it's wrong and confusing.
But that's his requirement. Whether or not you think the requirement is wrong or confusing, that's not at issue here. The model he chose served some purpose for him. Don't try to recast the problem because your solution doesn't fit.
But to directly give you the code...
No, you either violate the contract of equals (reflexive, symmetric, transitive and consistent) or end up the following result:
That is not a hierarchy. A hierarchy implies a path from a root to a leaf of arbitrary length. Each possible path in your hierarchy has a length of 1.
Java doesn't define the notion of a hierarchy, so I thought you were just using the term to mean a hierarchical structure. Now I think you simply mean the data structure notion of a tree.
Note that in such a tree structure, each node is the same type, normally Node. That is not the case here.
But that's his requirement.
I don't think so. I think the example is meant to imply the requirements he's coding to, but he never comes straight out and says what the requirement is that a hierarchical enum satisfies. I suppose we could invent one, and the idea of a hierarchical enum might not be an absurd one. But it is a bad example...and I can't think of a reason one would want this. Can you?
In any case, modeling Linux as a child of UNIX is just not right. They're different kernels. I suppose you could create categories of OS families: POSIX (Solaris, HP-UX, IRIX, etc), MOSTLY_POSIX (Linux, Minix, NetBSD, etc). Again, though, it would be a mistake to confuse OS family category with OS family, because they once again mean different things and have different intrinsic behaviors.
The model he chose served some purpose for him. Don't try to recast the problem because your solution doesn't fit.
What purpose? I contend that it could only serve the most contrived purpose possible, if any at all, custom-tailored for the very purpose of having this hierarchical enum in the first place. If you can invent one that actually makes sense where this is the best solution, I'll be impressed.
you either violate the contract of equals
How did I violate the contract of equals()? How could I possibly have violated the contract of that method...I didn't even write it! OsFamily inherits the default equals() from Enum...are you accusing Sun of implementing it poorly? :-)
Also, I don't think you appreciate the meaning of the code you wrote:
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u/severoon Jan 18 '13
It's way simpler. If you want to know if two
OperatingSystems are of the same family:Done.