Nesting enums in Java

Question

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 v

Answer 1

As I understand enums, they are kind of singletons. It means enum X {A,B} has two singleton instances A,B. If you had nested enum A { P, Q }, how you can say if X.A is X.A.P or X.A.Q ? I wish I was able to say it more simply.

Use static class.

Answer 2

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;

Answer 3

Nesting enums is not possible. But enums can implement interfaces. Why not have A and B as two different enums that both implement a TypedEnum interface with getType() and getValue() methods?