Java enums - choice between fields, abstract methods, and class level map

Question

I have written a Java enum where the values have various attributes. These attributes could be stored in any of the following ways:

Using fields:

enum Eenum {
  V1(p1),
  V2(p2);

  private final A attr;

  public A attr() { return attr; }

  private Eenum(A attr) {
    this.attr = attr;
  }
}

Using abstract methods:

enum Eenum {
  V1 {
    public A attr() { return p1; }
  },

  V2 {
    public A attr() { return p2; }
  }

  public abstract A attr();
}

Using class level map:

enum Eenum {
  V1,
  V2;

  public A attr() { return attrs.get(this); }

  private static final Map<Eenum, A> attrs;

  static {
    ImmutableMap.Builder<Eenum, A> builder = ImmutableMap.builder();
    builder.put(V1, p1);
    builder.put(V2, p2);
    attrs = builder.build();
  }
}

How should I decide when to prefer which?

Thanks!

Answer 1

I would do the one which you think is the simplest.

In general I don't write code which can be implemented using data. I would use the first one.

My actual use case has some attributes which are not relevant for all enum values

You can use a combination of these approaches if it makes sense on a per attribute basis.

A fourth option is to not have an abstract method.

enum Eenum {
  V1 {
    public A attr() { return p1; }
  },

  V2 {
    public A attr() { return p2; }
  }, 
  V3, V4, V5, V6;

  public A attr() { return defaultA; }
}