Conveniently map between enum and int / String

Question

When working with variables/parameters that can only take a finite number of values, I try to always use Java\'s enum, as in

public enum BonusT         


        

Answer 1

Both the .ordinal() and values()[i] are unstable since they are dependent to the order of enums. Thus if you change the order of enums or add/delete some your program would break.

Here is a simple yet effective method to map between enum and int.

public enum Action {
    ROTATE_RIGHT(0), ROTATE_LEFT(1), RIGHT(2), LEFT(3), UP(4), DOWN(5);

    public final int id;
    Action(int id) {
        this.id = id;
    }

    public static Action get(int id){
        for (Action a: Action.values()) {
            if (a.id == id)
                return a;
        }
        throw new IllegalArgumentException("Invalid id");
    }
}

Applying it for strings shouldn't be difficult.

Answer 2

You could perhaps use something like

interface EnumWithId {
    public int getId();

}


enum Foo implements EnumWithId {

   ...
}

That would reduce the need for reflection in your utility class.

Answer 3

given:

public enum BonusType { MONTHLY(0), YEARLY(1), ONE_OFF(2) }

BonusType bonus = YEARLY;

System.out.println(bonus.Ordinal() + ":" + bonus)

Output: 1:YEARLY

Answer 4

I'm not sure if it's the same in Java, but enum types in C are automatically mapped to integers as well so you can use either the type or integer to access it. Have you tried simply accessing it with integer yet?

Answer 5

For the sake of completeness, here is a generic approach to retrieve enum values by index from any enum type. My intention was to make the method look and feel like Enum.valueOf(Class, String). Fyi, i copied this method from here.

Index related issues (already discussed in depth here) still apply.

/**
 * Returns the {@link Enum} instance for a given ordinal.
 * This method is the index based alternative
 * to {@link Enum#valueOf(Class, String)}, which
 * requires the name of an instance.
 * 
 * @param <E> the enum type
 * @param type the enum class object
 * @param ordinal the index of the enum instance
 * @throws IndexOutOfBoundsException if ordinal < 0 || ordinal >= enums.length
 * @return the enum instance with the given ordinal
 */
public static <E extends Enum<E>> E valueOf(Class<E> type, int ordinal) {
    Preconditions.checkNotNull(type, "Type");
    final E[] enums = type.getEnumConstants();
    Preconditions.checkElementIndex(ordinal, enums.length, "ordinal");
    return enums[ordinal];
}

Answer 6

Int -->String :

public enum Country {

    US("US",0),
    UK("UK",2),
    DE("DE",1);


    private static Map<Integer, String> domainToCountryMapping; 
    private String country;
    private int domain;

    private Country(String country,int domain){
        this.country=country.toUpperCase();
        this.domain=domain;
    }

    public String getCountry(){
        return country;
    }


    public static String getCountry(String domain) {
        if (domainToCountryMapping == null) {
            initMapping();
        }

        if(domainToCountryMapping.get(domain)!=null){
            return domainToCountryMapping.get(domain);
        }else{
            return "US";
        }

    }

     private static void initMapping() {
         domainToCountryMapping = new HashMap<Integer, String>();
            for (Country s : values()) {
                domainToCountryMapping.put(s.domain, s.country);
            }
        }