How to get additional attribute of enum value?

Question

In my chat application I have an enum:

enum ContactRelationType {
  Friend,
  Familiar,
  Ignored,
  Unknown,  
  Guild,
  Officers,
  Academy,
  Community,
  System
}

Half of ContactRelationType values are rooms (Guild, Officers, Academy, Community, System). I need to know is the value room or not.

I know three ways to do it:

The first:

enum ContactRelationType {
  Friend,
  Familiar,
  Ignored,
  Unknown,  
  Guild,
  Officers,
  Academy,
  Community,
  System;

    public boolean isRoom() {
    return this == Guild ||
        this == Officers ||
        this == Academy ||
        this == Community ||
        this == System;
  }
}

It looks ugly and the IDEA tells me "Overly complex boolean expression" and it is.

The second:

    enum ContactRelationType {
      Friend,
      Familiar,
      Ignored,
      Unknown,  
      Guild,
      Officers,
      Academy,
      Community,
      System;

    public boolean isRoom() {
      switch (this) {
        case Guild:
        case Officers:
        case Academy:
        case Community:
        case System:
          return true;
        default:
          return false;
    }
}

it looks ugly too.

The third:

    public enum ContactRelationType {
      Friend(false),
      Familiar(false),
      Ignored(false),
      Unknown(false),
      Guild(true),
      Officers(true),
      Academy(true),
      Community(true),
      System(true);

      private boolean room;

      ContactRelationType(boolean room) {
        this.room = room;
      }

      public boolean isRoom() {
        return room;
      }
}

But in this case I have boolean room in all enum instances.

So, what solution is better and why?

Answer 1

You solution with boolean flag is good. Just add a default constructor:

 ContactRelationType() {
    this(false);
  }

Now you do not have to write true or false for each enum member; only for those that are not "default":

public enum ContactRelationType {
  Friend,
  Familiar,
  Ignored,
  Unknown,
  Guild(true),
  Officers(true),
  Academy(true),
  Community(true),
  System(true);

Answer 2

You probably could use an EnumSet. They are very efficiently implemented with a BitSet equivalent.

enum ContactRelationType {

    Friend,
    Familiar,
    Ignored,
    Unknown,
    Guild,
    Officers,
    Academy,
    Community,
    System;

    public boolean isRoomRelation() {
        return RoomContacts.contains(this);
    }
}

static final Set<ContactRelationType> RoomContacts = EnumSet.of(
        ContactRelationType.Guild,
        ContactRelationType.Officers,
        ContactRelationType.Academy,
        ContactRelationType.Community,
        ContactRelationType.System);