Is there a way in Java to declare an enumeration whose values can be used together? For example:
enum FileAccess { Read, Write, ReadWrite }
Is it possible to define ReadWrite as Read | Write (or anything that would yield the same result)?
views:
898answers:
2
+15
A:
You use EnumSet:
EnumSet<FileAccess> readWrite = EnumSet.of(FileAccess.Read, FileAccess.Write);
This is actually somewhat more elegant than the C#/.NET way, IMO - aside from anything else, you can easily distinguish between a set and a single value.
Jon Skeet
2009-01-02 13:58:17
Can you explain how you'd use this EnumSet to produce a read/write constant?
Paul Tomblin
2009-01-02 14:02:30
Exactly in the way I've shown - just make it a final variable. EnumSet is immutable.
Jon Skeet
2009-01-02 14:06:23
But that gives you a Set, not an Enum, or indeed an integer that you could store in a database (like Enum.ordinal()).
Paul Tomblin
2009-01-02 14:14:24
If you want an external (DB) representation than bare enums are unacceptable -- using ordinals is a bad idea for maintainance reasons. After adding a external representation to your enums, add a wrapper around EnumSet to manage the combined external representation in both directions.
Darron
2009-01-02 14:20:38
Thanks Darron, this summarizes what I was looking for.
Hosam Aly
2009-01-02 14:24:22
+2
A:
See EnumSet which allows you to do this efficiently:
EnumSet set = EnumSet.of(READ, WRITE);
JodaStephen
2009-01-02 13:58:49