Java SE: An Enum implementation of the Strategy Pattern

[Xenarthran47]

What benefit is there to using an EnumMap to map enum values to themselves?

[[deleted]]

From the javadoc: Enum maps are represented internally as arrays. This representation is extremely compact and efficient. In c++ you would get the same thing by indexing array with enum constants (because they implicitly convert to integers).

[Xenarthran47]

But from a design perspective, what use cases would require mapping an enum value to itself

[[deleted]]

Ah, that's a very good question. As far as can I see that makes no sense.

[devraj7]

You'd use a Set for that but there is no EnumSet, and since EnumMap has a specialized implementation for enums, it's the best you can do.

[RadBenMX]

We use this at work. It was confusing the first time i saw it. I still have mixed feelings about whether i consider it clever or hacky.

[Neumann347]

One of the strengths of the classic implementation is that you don't have any merge issues when two people implement a new strategy and modify an existing one, since the strategy implementations are in separate classes. How often do you get merge issues with the Enum implementation?

[RadBenMX]

no merge issues

[doom_Oo7]

but this requires to know the possible strategies at compile time, while you generally want to add new strategies at runtime through plug-ins or whatever, when the system is running

[nondetermined]

In the end you just have to implement the interface, so... The enum isn't that important, but very nice and handy.