I want to nest some enums. The object i'm representing are Flags, with a type, and a value. There are a discrete number of types, and each type has a distinct set of possible values.
So if Type A can have values 1, 2 or 3, and Type B can have values 4,5,6, I'd like to be able to do things like:
Flag f = Flag.A.1;
f.getType() - returns "A"
f.getValue() - returns "1"
Flag f2 = Flag.A.4; -- Syntax error.
I'm driving myself crazy trying to nest enums within enums - is what i'm trying possible - do I need to ditch enums altogether and handcraft a static class with static members?
My best effort so far is:
public class Flag {
enum A extends Flag {
ONE("ONE"),
TWO("TWO"),
THREE("THREE");
private A(String value) {
Flag.type = "A";
Flag.value = value;
}
}
private static String type;
private static String value;
}
But if I do:
Flag f = Flag.A.ONE;
The types are incompatible.
解決方案
You cannot have a number as an enum. It has to be an identifier.
You can do this
interface Flag {
String getType();
int getValue();
enum A implements Flag{
one, two, three;
String getType() { return getClass().getSimpleName(); }
int getvalue() { return ordinal()+1; }
}
enum B implements Flag{
four, five, six;
String getType() { return getClass().getSimpleName(); }
int getvalue() { return ordinal()+4; }
}
}
Flag f = Flag.A.one;
However a simpler option may be
enum Flag {
A1, A2, A3, B4, B5, B6;
public String getType() { return name().substring(0,1); }
public int getValue() { return name().charAt(1) - '0'; }
}
Flag f = Flag.A1;