What s the advantage of a Java enum versus a class with public static final fields

Question

I am very familiar with C  but starting to work more in Java  I expected to learn that enums in Java were basically equivalent to those in C  but apparently this is not the case  Initially I was excited to learn that Java enums could contain multiple pieces of data which seems very advantageous  http   docs oracle com javase tutorial java javaOO enum html   However  since then I have found a lot of features missing that are trivial in C   such as the ability to easily assign an enum element a certain value  and consequently the ability to convert an integer to an enum without a decent amount of effort  i e  Convert integer value to matching Java Enum    So my question is this  is there any benefit to Java enums over a class with a bunch of public static final fields  Or does it just provide more compact syntax   EDIT  Let me be more clear  What is the benefit of Java enums over a class with a bunch of public static final fields of the same type  For example  in the planets example at the first link  what is the advantage of an enum over a class with these public constants   public static final Planet MERCURY   new Planet 3 303e 23  2 4397e6   public static final Planet VENUS   new Planet 4 869e 24  6 0518e6   public static final Planet EARTH   new Planet 5 976e 24  6 37814e6   public static final Planet MARS   new Planet 6 421e 23  3 3972e6   public static final Planet JUPITER   new Planet 1 9e 27  7 1492e7   public static final Planet SATURN   new Planet 5 688e 26  6 0268e7   public static final Planet URANUS   new Planet 8 686e 25  2 5559e7   public static final Planet NEPTUNE   new Planet 1 024e 26  2 4746e7     As far as I can tell  casablanca s answer is the only one that satisfies this

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There are many good answers here  but none mentiones that there are highly optimized implementations of the Collection API classes interfaces specifically for enums    EnumSet EnumMap   These enum specific classes only accept Enum instances  the EnumMap only accept Enums only as keys   and whenever possible  they revert to compact representation and bit manipulation in their implementation   What does this mean   If our Enum type has no more that 64 elements  most of real-life Enum examples will qualify for this   the implementations store the elements in a single long value  each Enum instance in question will be associated with a bit of this 64-bit long long  Adding an element to an EnumSet is simply just setting the proper bit to 1  removing it is just setting that bit to 0  Testing if an element is in the Set is just one bitmask test  Now you gotta love Enums for this

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enum Benefits   Enums are type-safe  static fields are not There is a finite number of values  it is not possible to pass non-existing enum value  If you have static class fields  you can make that mistake  Each enum can have multiple properties  fields getters  assigned - encapsulation  Also some simple methods  YEAR toSeconds   or similar  Compare  Colors RED getHex   with Colors toHex Colors RED    quot such as the ability to easily assign an enum element a certain value quot  enum EnumX    VAL 1 1     VAL 200 200     public final int certainValue    private X int certainValue  this certainValue   certainValue       quot and consequently the ability to convert an integer to an enum without a decent amount of effort quot  Add a method converting int to enum which does that  Just add static HashMap lt Integer  EnumX gt  containing the mapping java enum  If you really want to convert ord VAL 200 ordinal   back to val 200 just use  EnumX values   ord

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Nobody mentioned the ability to use them in switch statements  I ll throw that in as well   This allows arbitrarily complex enums to be used in a clean way without using instanceof  potentially confusing if sequences  or non-string int switching values  The canonical example is a state machine

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I think an enum can t be final  because under the hood compiler generates subclasses for each enum entry   More information From source

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Type safety and value safety  Guaranteed singleton  Ability to define and override methods  Ability to use values in switch statement case statements without qualification  Built-in sequentialization of values via ordinal    Serialization by name not by value  which offers a degree of future-proofing  EnumSet and EnumMap classes

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Technically one could indeed view enums as a class with a bunch of typed constants  and this is in fact how enum constants are implemented internally  Using an enum however gives you useful methods  Enum javadoc  that you would otherwise have to implement yourself  such as Enum valueOf

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example   public class CurrencyDenom      public static final int PENNY   1   public static final int NICKLE   5   public static final int DIME   10  public static final int QUARTER   25     Limitation of java Constants  1  No Type-Safety  First of all it   s not type-safe  you can assign any valid int value to int e g  99 though there is no coin to represent that value   2  No Meaningful Printing  printing value of any of these constant will print its numeric value instead of meaningful name of coin e g  when you print NICKLE it will print  5  instead of  NICKLE   3  No namespace  to access the currencyDenom constant we need to prefix class name e g  CurrencyDenom PENNY instead of just using PENNY though this can also be achieved by using static import in JDK 1 5  Advantage of enum  1  Enums in Java are type-safe and has there own name-space  It means your enum will have a type for example  Currency  in below example and you can not assign any value other than specified in Enum Constants   public enum Currency  PENNY  NICKLE  DIME  QUARTER     Currency coin   Currency PENNY  coin   1    compilation error  2  Enum in Java are reference type like class or interface and you can define constructor  methods and variables inside java Enum which makes it more powerful than Enum in C and C   as shown in next example of Java Enum type   3  You can specify values of enum constants at the creation time as shown in below example  public enum Currency  PENNY 1   NICKLE 5   DIME 10   QUARTER 25    But for this to work you need to define a member variable and a constructor because PENNY  1  is actually calling a constructor which accepts int value   see below example   public enum Currency       PENNY 1   NICKLE 5   DIME 10   QUARTER 25       private int value       private Currency int value                this value   value              Reference  https   javarevisited blogspot com 2011 08 enum-in-java-example-tutorial html

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The primary advantage is type safety  With a set of constants  any value of the same intrinsic type could be used  introducing errors   With an enum only the applicable values can be used   For example  public static final int SIZE SMALL    1  public static final int SIZE MEDIUM   2  public static final int SIZE LARGE    3   public void setSize int newSize           obj setSize 15      Compiles but likely to fail later   vs  public enum Size   SMALL  MEDIUM  LARGE     public void setSize Size s           obj setSize          Can t even express the above example with an enum

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An enum is implictly final  with a private constructors  all its values are of the same type or a sub-type  you can obtain all its values using values    gets its name   or ordinal   value or you can look up an enum by number or name   You can also define subclasses  even though notionally final  something you can t do any other way   enum Runner implements Runnable       HI          public void run                System out println  Hello                    BYE          public void run                System out println  Sayonara                    public String toString                return  good-bye                       class MYRunner extends Runner    won t compile

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Another important difference is that java compiler treats static final fields of primitive types and String as literals  It means these constants become inline  It s similar to C C    define preprocessor  See this SO question  This is not the case with enums

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You get compile time checking of valid values when you use an enum   Look at this question

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The first benefit of enums  as you have already noticed  is syntax simplicity  But the main point of enums is to provide a well-known set of constants which  by default  form a range and help to perform more comprehensive code analysis through type  amp  value safety checks   Those attributes of enums help both a programmer and a compiler  For example  let s say you see a function that accepts an integer  What that integer could mean  What kind of values can you pass in  You don t really know right away  But if you see a function that accepts enum  you know very well all possible values you can pass in   For the compiler  enums help to determine a range of values and unless you assign special values to enum members  they are well ranges from 0 and up  This helps to automatically track down errors in the code through type safety checks and more  For example  compiler may warn you that you don t handle all possible enum values in your switch statement  i e  when you don t have default case and handle only one out of N enum values   It also warns you when you convert an arbitrary integer into enum because enum s range of values is less than integer s and that in turn may trigger errors in the function that doesn t really accept an integer  Also  generating a jump table for the switch becomes easier when values are from 0 and up   This is not only true for Java  but for other languages with a strict type-checking as well  C  C    D  C  are good examples

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Main reason  Enums help you to write well-structured code where the semantic meaning of parameters is clear and strongly-typed at compile time - for all the reasons other answers have given   Quid pro quo  in Java out of the box  an Enum s array of members is final   That s normally good as it helps value safety and testing  but in some situations it could be a drawback  for example if you are extending existing base code perhaps from a library  In contrast  if the same data is in a class with static fields you can easily add new instances of that class at runtime  you might also need to write code to add these to any Iterable you have for that class    But this behaviour of Enums can be changed  using reflection you can add new members at runtime or replace existing members  though this should probably only be done in specialised situations where there is no alternative  i e  it s a hacky solution and may produce unexpected issues  see my answer on Can I add and remove elements of enumeration at runtime in Java

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There is less confusion  Take Font for instance  It has a constructor that takes the name of the Font you want  its size and its style  new Font String  int  int    To this day I cannot remember if style or size goes first  If Font had used an enum for all of its different styles  PLAIN  BOLD  ITALIC  BOLD ITALIC   its constructor would look like Font String  Style  int   preventing any confusion  Unfortunately  enums weren t around when the Font class was created  and since Java has to maintain reverse compatibility  we will always be plagued by this ambiguity   Of course  this is just an argument for using an enum instead of public static final constants  Enums are also perfect for singletons and implementing default behavior while allowing for later customization  I E  the strategy pattern   An example of the latter is java nio file s OpenOption and StandardOpenOption  if a developer wanted to create his own non-standard OpenOption  he could

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There are many advantages of enums that are posted here  and I am creating such enums right now as asked in the question  But I have an enum with 5-6 fields   enum Planet  EARTH 1000000  312312321 31232131   some text       12        other planets        In these kinds of cases  when you have multiple fields in enums  it is much difficult to understand which value belongs to which field as you need to see constructor and eye-ball    Class with static final constants and using Builder pattern to create such objects makes it more readable  But  you would lose all other advantages of using an enum  if you need them   One disadvantage of such classes is  you need to add the Planet objects manually to the list set of Planets   I still prefer enum over such class  as values   comes in handy and you never know if you need them to use in switch or EnumSet or EnumMap in future

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The biggest advantage is enum Singletons are easy to write and thread-safe    public enum EasySingleton      INSTANCE      and        Singleton pattern example with Double checked Locking    public class DoubleCheckedLockingSingleton       private volatile DoubleCheckedLockingSingleton INSTANCE        private DoubleCheckedLockingSingleton           public DoubleCheckedLockingSingleton getInstance             if INSTANCE    null               synchronized DoubleCheckedLockingSingleton class                     double checking Singleton instance                 if INSTANCE    null                       INSTANCE   new DoubleCheckedLockingSingleton                                                        return INSTANCE             both are similar and it handled Serialization by themselves by implementing      readResolve to prevent another instance of Singleton     private Object readResolve            return INSTANCE          more

[java] What's the advantage of a Java enum versus a class with public static final fields?

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