The following Java code is legal, believe it or not:
public enum MyEnum { INST1() { public void foo() { //... } }, INST2...; }
What the f…?!
Moshe, my student, is working on some Java parser. You really learn a language when you parse it. Following some question that he had, we found out about the code above. His reaction was less mild then just “what the…” – He nearly freaked out out, and rightfully so.
The rationale behind this piece of code is:
- Enums in Java are just classes with some syntactic sugar
- Enum constants are instances of the enum class
- An instance declaration in Java may include an inner anonymous class declaration
- → Enum constants may include a class body
Having enumerated constants with their-own class body is apparently a coherent part of the Java language. One can argue, though, how useful or readable this language feature is.
I usually don’t like programming languages impersonation jokes, but replying to this “if programming languages were relationships” post: When I started “dating” Java, it was “the little language that could”. 10 years after, it’s “one big mother” with a whole range of offsprings. With due respect to “all things J”, like JAX-WS, JAXB/StAX, and a whole range of other JSRs – There’s something to say in favour of simplicity too.
(This post was cleared of nasty chauvinistic insinuations toward a female impersonation of Java and other JVM-based programming languages. I hope you appreciate it.)
Actually, I find it very natural.
To me, enums are a way to implement the Strategy pattern:
…
switch (decideAction(args))
{
case GoHome: … break;
case AnotherBeer: … break;
}
etc.
So the Java enums are just a very cool way to do it:
public enum WhatToDo
{
GoHome {@Override void act() { /*walking…*/ }},
AnotherBeer {@Override void act() { /*drinking…*/ }};
abstract void act();
}
….
decideAction(args).act();
…
I think this is a major part of what enums are for.
I had serious convulsions while writing that code.
But it’s over now, and I don’t wish to talk about it anymore. I will bear these scars forever.
Aviv:
I agree writing this little Strategy piece in separate classes will be a bit more tedious, but just a tiny wee bit. Not enough to discard it in favor of the of the enum – for brevity’s sake.
So true. Honesty and everything reconigezd.