Pick a random value from an enum

Question

If I have an enum like this   public enum Letter       A      B      C                What is the best way to pick one randomly  It doesn t need to be production quality bulletproof  but a fairly even distribution would be nice   I could do something like this  private Letter randomLetter         int pick   new Random   nextInt Letter values   length       return Letter values   pick       But is there a better way  I feel like this is something that s been solved before

User · Answer

Agree with Stphen C  amp  helios  Better way to fetch random element from Enum is    public enum Letter     A    B    C             private static final Letter   VALUES   values      private static final int SIZE   VALUES length    private static final Random RANDOM   new Random       public static Letter getRandomLetter          return VALUES RANDOM nextInt SIZE

User · Answer

A single method is all you need for all your random enums       public static  lt T extends Enum lt   gt  gt  T randomEnum Class lt T gt  clazz           int x   random nextInt clazz getEnumConstants   length           return clazz getEnumConstants   x           Which you ll use   randomEnum MyEnum class     I also prefer to use SecureRandom as   private static final SecureRandom random   new SecureRandom

User · Answer

I would use this   private static Random random   new Random     public Object getRandomFromEnum Class lt   extends Enum lt   gt  gt  clazz        return clazz values   random nextInt clazz values   length

User · Answer

If you do this for testing you could use Quickcheck  this is a Java port I ve been working on     import static net java quickcheck generator PrimitiveGeneratorSamples     TimeUnit anyEnumValue   anyEnumValue TimeUnit class     one value   It supports all primitive types  type composition  collections  different distribution functions  bounds etc  It has support for runners executing multiple values   import static net java quickcheck generator PrimitiveGeneratorsIterables     for TimeUnit timeUnit   someEnumValues TimeUnit class            test multiple values     The advantage of Quickcheck is that you can define tests based on a specification where plain TDD works with scenarios

User · Answer

Single line   return Letter values   new Random   nextInt Letter values   length

User · Answer

Combining the suggestions of cletus and helios   import java util Random   public class EnumTest        private enum Season   WINTER  SPRING  SUMMER  FALL        private static final RandomEnum lt Season gt  r           new RandomEnum lt Season gt  Season class        public static void main String   args            System out println r random                private static class RandomEnum lt E extends Enum lt E gt  gt             private static final Random RND   new Random            private final E   values           public RandomEnum Class lt E gt  token                values   token getEnumConstants                       public E random                 return values RND nextInt values length                        Edit  Oops  I forgot the bounded type parameter   lt E extends Enum lt E gt  gt

User · Answer

Letter lettre   Letter values    int  Math random   Letter values   length

User · Answer

I guess that this single-line-return method is efficient enough to be used in such a simple job  public enum Day       SUNDAY      MONDAY      THURSDAY      WEDNESDAY      TUESDAY      FRIDAY       public static Day getRandom             return values    int   Math random     values   length               public static void main String   args            System out println Day getRandom

User · Answer

Here a version that uses shuffle and streams  List lt Direction gt  letters   Arrays asList Direction values     Collections shuffle letters   return letters stream   findFirst   get

User · Answer

It  s eaiser to implement an random function on the enum   public enum Via       A  B   public static Via viaAleatoria        Via   vias   Via values        Random generator   new Random        return vias generator nextInt vias length              and then you call it from the class you need it like this  public class Guardia  private Via viaActiva   public Guardia        viaActiva   Via viaAleatoria

User · Answer

The only thing I would suggest is caching the result of values   because each call copies an array  Also  don t create a Random every time  Keep one  Other than that what you re doing is fine  So   public enum Letter     A    B    C             private static final List lt Letter gt  VALUES       Collections unmodifiableList Arrays asList values        private static final int SIZE   VALUES size      private static final Random RANDOM   new Random       public static Letter randomLetter          return VALUES get RANDOM nextInt SIZE

User · Answer

Simple Kotlin Solution  MyEnum values   random     random   is a default extension function included in base Kotlin on the Collection object  Kotlin Documentation Link  If you d like to simplify it with an extension function  try this   inline fun  lt reified T   Enum lt T gt  gt  random    T   enumValues lt T gt    random       Then call random lt MyEnum gt      To make it static on your enum class  Make sure to import my package random in your enum file  MyEnum randomValue       Add this to your enum class companion object       fun randomValue    MyEnum           return random             If you need to do it from an instance of the enum  try this extension  inline fun  lt reified T   Enum lt T gt  gt  T random     enumValues lt T gt    random       Then call MyEnum VALUE random      or myEnumVal random

User · Answer

This is probably the most concise way of achieving your goal All you need to do is to call Letter getRandom   and you will get a random enum letter   public enum Letter       A      B      C                 public static Letter getRandom             return values    int   Math random     values   length

User · Answer

It s probably easiest to have a function to pick a random value from an array   This is more generic  and is straightforward to call    lt T gt  T randomValue T   values        return values mRandom nextInt values length        Call like so   MyEnum value   randomValue MyEnum values

[java] Pick a random value from an enum?

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