Check if enum exists in Java

Question

Is there anyway to check if an enum exists by comparing it to a given string  I can t seem to find any such function  I could just try to use the valueOf method and catch an exception but I v been taught that catching runtime exceptions is not good practice  Anybody have any ideas

User · Answer

One of my favorite lib  Apache Commons   The EnumUtils can do that easily    Following an example to validate an Enum with that library   public enum MyEnum       DIV  div    DEPT  dept    CLASS  class         private final String val       MyEnum String val        this val   val             public String getVal         return val            MyEnum strTypeEnum   null      test if String str is compatible with the enum     e g  if you pass str    div   it will return false  If you pass  DIV   it will return true  if  EnumUtils isValidEnum MyEnum class  str         strTypeEnum   MyEnum valueOf str

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Based on Jon Skeet answer i ve made a class that permits to do it easily at work   import com google common collect ImmutableMap  import com google common collect Maps   import java util EnumSet  import java util HashSet  import java util Map  import java util Set           lt p gt     This permits to easily implement a failsafe implementation of the enums s valueOf    Better use it inside the enum so that only one of this object instance exist for each enum        a cache could solve this if needed      lt  p gt         lt p gt     Basic usage exemple on an enum class called MyEnum          private static final FailSafeValueOf lt MyEnum gt  FAIL SAFE   FailSafeValueOf create MyEnum class        public static MyEnum failSafeValueOf String enumName             return FAIL SAFE valueOf enumName                 lt  p gt         lt p gt     You can also use it outside of the enum this way       FailSafeValueOf create MyEnum class  valueOf  EnumName        lt  p gt         author Sebastien Lorber  lt i gt  lorber sebastien gmail com  lt  i gt      public class FailSafeValueOf lt T extends Enum lt T gt  gt         private final Map lt String T gt  nameToEnumMap       private FailSafeValueOf Class lt T gt  enumClass            Map lt String T gt  map   Maps newHashMap            for   T value   EnumSet allOf enumClass                 map put  value name     value                     nameToEnumMap   ImmutableMap copyOf map                         Returns the value of the given enum element        If the          param enumName         return             public T valueOf String enumName            return nameToEnumMap get enumName              public static  lt U extends Enum lt U gt  gt  FailSafeValueOf lt U gt  create Class lt U gt  enumClass            return new FailSafeValueOf lt U gt  enumClass              And the unit test   import org testng annotations Test   import static org testng Assert              author Sebastien Lorber  lt i gt  lorber sebastien gmail com  lt  i gt      public class FailSafeValueOfTest        private enum MyEnum           TOTO          TATA                     private static final FailSafeValueOf lt MyEnum gt  FAIL SAFE   FailSafeValueOf create MyEnum class           public static MyEnum failSafeValueOf String enumName                return FAIL SAFE valueOf enumName                         Test     public void testInEnum             assertNotNull  MyEnum failSafeValueOf  TOTO              assertNotNull  MyEnum failSafeValueOf  TATA              assertNull  MyEnum failSafeValueOf  TITI                  Test     public void testInApp             assertNotNull  FailSafeValueOf create MyEnum class  valueOf  TOTO              assertNotNull  FailSafeValueOf create MyEnum class  valueOf  TATA              assertNull  FailSafeValueOf create MyEnum class  valueOf  TITI                 Notice that i used Guava to make an ImmutableMap but actually you could use a normal map i think since the map is never returned

User · Answer

You can also use Guava and do something like this      This method returns enum for a given string if it exists  otherwise it returns default enum  private MyEnum getMyEnum String enumName         It is better to return default instance of enum instead of null   return hasMyEnum enumName    MyEnum valueOf enumName    MyEnum DEFAULT        This method checks that enum for a given string exists  private boolean hasMyEnum String enumName      return Iterables any Arrays asList MyEnum values     new Predicate lt MyEnum gt          public boolean apply MyEnum myEnum          return myEnum name   equals enumName                    In second method I use guava  Google Guava  library which provides very useful Iterables class  Using the Iterables any   method we can check if a given value exists in a list object  This method needs two parameters  a list and Predicate object  First I used Arrays asList   method to create a list with all enums  After that I created new Predicate object which is used to check if a given element  enum in our case  satisfies the condition in apply method  If that happens  method Iterables any   returns true value

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If I need to do this  I sometimes build a Set lt String gt  of the names  or even my own Map lt String MyEnum gt  - then you can just check that   A couple of points worth noting    Populate any such static collection in a static initializer  Don t use a variable initializer and then rely on it having been executed when the enum constructor runs - it won t have been   The enum constructors are the first things to be executed  before the static initializer   Try to avoid using values   frequently - it has to create and populate a new array each time  To iterate over all elements  use EnumSet allOf which is much more efficient for enums without a large number of elements    Sample code   import java util     enum SampleEnum       Foo      Bar       private static final Map lt String  SampleEnum gt  nameToValueMap           new HashMap lt String  SampleEnum gt          static           for  SampleEnum value   EnumSet allOf SampleEnum class                 nameToValueMap put value name    value                        public static SampleEnum forName String name            return nameToValueMap get name            public class Test       public static void main String    args          throws Exception      Just for simplicity          System out println SampleEnum forName  Foo             System out println SampleEnum forName  Bar             System out println SampleEnum forName  Baz               Of course  if you only have a few names this is probably overkill - an O n  solution often wins over an O 1  solution when n is small enough  Here s another approach   import java util     enum SampleEnum       Foo      Bar          We know we ll never mutate this  so we can keep        a local copy      private static final SampleEnum   copyOfValues   values         public static SampleEnum forName String name            for  SampleEnum value   copyOfValues                if  value name   equals name                     return value                                  return null           public class Test       public static void main String    args          throws Exception      Just for simplicity          System out println SampleEnum forName  Foo             System out println SampleEnum forName  Bar             System out println SampleEnum forName  Baz

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Most of the answers suggest either using a loop with equals to check if the enum exists or using try catch with enum valueOf    I wanted to know which method is faster and tried it  I am not very good at benchmarking  so please correct me if I made any mistakes   Heres the code of my main class       package enumtest   public class TestMain        static long timeCatch  timeIterate      static String checkFor      static int corrects       public static void main String   args            timeCatch   0          timeIterate   0          TestingEnum   enumVals   TestingEnum values            String   testingStrings   new String enumVals length   5           for  int j   0  j  lt  10000  j                  for  int i   0  i  lt  testingStrings length  i                      if  i   5    0                        testingStrings i    enumVals i   5  toString                      else                       testingStrings i     DOES NOT EXIST    i                                               for  String s   testingStrings                    checkFor   s                  if  tryCatch                            corrects                                    if  iterate                            corrects                                                     System out println timeCatch   1000    us for try catch            System out println timeIterate   1000    us for iterate            System out println corrects              static boolean tryCatch             long timeStart  timeEnd          timeStart   System nanoTime            try               TestingEnum valueOf checkFor               return true            catch  IllegalArgumentException e                return false            finally               timeEnd   System nanoTime                timeCatch    timeEnd - timeStart                        static boolean iterate             long timeStart  timeEnd          timeStart   System nanoTime            TestingEnum   values   TestingEnum values            for  TestingEnum v   values                if  v toString   equals checkFor                     timeEnd   System nanoTime                    timeIterate    timeEnd - timeStart                  return true                                  timeEnd   System nanoTime            timeIterate    timeEnd - timeStart          return false            This means  each methods run 50000 times the lenght of the enum I ran this test multiple times  with 10  20  50 and 100 enum constants  Here are the results    10  try catch  760ms   iteration  62ms 20  try catch  1671ms   iteration  177ms 50  try catch  3113ms   iteration  488ms 100  try catch  6834ms   iteration  1760ms   These results were not exact  When executing it again  there is up to 10  difference in the results  but they are enough to show  that the try catch method is far less efficient  especially with small enums

User · Answer

I don t know why anyone told you that catching runtime exceptions was bad   Use valueOf and catching IllegalArgumentException is fine for converting checking a string to an enum

User · Answer

I don t think there s a built-in way to do it without catching exceptions  You could instead use something like this   public static MyEnum asMyEnum String str        for  MyEnum me   MyEnum values              if  me name   equalsIgnoreCase str               return me            return null      Edit  As Jon Skeet notes  values   works by cloning a private backing array every time it is called  If performance is critical  you may want to call values   only once  cache the array  and iterate through that   Also  if your enum has a huge number of values  Jon Skeet s map alternative is likely to perform better than any array iteration

User · Answer

Since Java 8  we could use streams instead of for loops  Also  it might be apropriate to return an Optional if the enum does not have an instance with such a name   I have come up with the following three alternatives on how to look up an enum   private enum Test       TEST1  TEST2       public Test fromNameOrThrowException String name            return Arrays stream values                     filter e - gt  e name   equals name                    findFirst                    orElseThrow    - gt  new IllegalArgumentException  No enum with name     name               public Test fromNameOrNull String name            return Arrays stream values    filter e - gt  e name   equals name   findFirst   orElse null              public Optional lt Test gt  fromName String name            return Arrays stream values    filter e - gt  e name   equals name   findFirst

User · Answer

Just use valueOf   method  If the value doesn t exist  it throws IllegalArgumentException and you can catch it like that         boolean isSettingCodeValid   true          try               SettingCode valueOf settingCode toUpperCase               catch  IllegalArgumentException e                   throw custom exception or change the isSettingCodeValid value             isSettingCodeValid   false

[java] Check if enum exists in Java

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