What s the use of enum in Java

Question

So I looked into this  enum  type  and it kind of seems like a glorified array ArrayList List to me  What exactly is the use of it

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1  enum is a keyword in Object oriented method   2  It is used to write the code in a Single line  That s it not more than that        public class NAME                public static final String THUNNE               public static final String SHAATA                public static final String THULLU                -------This can be replaced by--------    enum NAME THUNNE  SHAATA  THULLU    3  Most of the developers do not use enum keyword  it is just a alternative method

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An enum type is a type whose fields consist of a fixed set of constants  Common examples include compass directions  values of NORTH  SOUTH  EAST  and WEST  and the days of the week   public enum Day       SUNDAY  MONDAY  TUESDAY  WEDNESDAY      THURSDAY  FRIDAY  SATURDAY      You should use enum types any time you need to represent a fixed set of constants  That includes natural enum types such as the planets in our solar system and data sets where you know all possible values at compile time   for example  the choices on a menu  command line flags  and so on   Here is some code that shows you how to use the Day enum defined above   public class EnumTest       Day day       public EnumTest Day day            this day   day             public void tellItLikeItIs             switch  day                case MONDAY                  System out println  Mondays are bad                     break               case FRIDAY                  System out println  Fridays are better                     break               case SATURDAY  case SUNDAY                  System out println  Weekends are best                     break               default                  System out println  Midweek days are so-so                     break                       public static void main String   args            EnumTest firstDay   new EnumTest Day MONDAY           firstDay tellItLikeItIs            EnumTest thirdDay   new EnumTest Day WEDNESDAY           thirdDay tellItLikeItIs            EnumTest fifthDay   new EnumTest Day FRIDAY           fifthDay tellItLikeItIs            EnumTest sixthDay   new EnumTest Day SATURDAY           sixthDay tellItLikeItIs            EnumTest seventhDay   new EnumTest Day SUNDAY           seventhDay tellItLikeItIs              The output is      Mondays are bad  Midweek days are so-so  Fridays are   better  Weekends are best  Weekends are best    Java programming language enum types are much more powerful than their counterparts in other languages  The enum declaration defines a class  called an enum type   The enum class body can include methods and other fields  The compiler automatically adds some special methods when it creates an enum  For example  they have a static values method that returns an array containing all of the values of the enum in the order they are declared  This method is commonly used in combination with the for-each construct to iterate over the values of an enum type  For example  this code from the Planet class example below iterates over all the planets in the solar system   for  Planet p   Planet values          System out printf  Your weight on  s is  f n                         p  p surfaceWeight mass        In addition to its properties and constructor  Planet has methods that allow you to retrieve the surface gravity and weight of an object on each planet  Here is a sample program that takes your weight on earth  in any unit  and calculates and prints your weight on all of the planets  in the same unit    public enum Planet       MERCURY  3 303e 23  2 4397e6       VENUS    4 869e 24  6 0518e6       EARTH    5 976e 24  6 37814e6       MARS     6 421e 23  3 3972e6       JUPITER  1 9e 27    7 1492e7       SATURN   5 688e 26  6 0268e7       URANUS   8 686e 25  2 5559e7       NEPTUNE  1 024e 26  2 4746e7        private final double mass       in kilograms     private final double radius     in meters     Planet double mass  double radius            this mass   mass          this radius   radius            private double mass     return mass        private double radius     return radius            universal gravitational constant   m3 kg-1 s-2      public static final double G   6 67300E-11       double surfaceGravity             return G   mass    radius   radius             double surfaceWeight double otherMass            return otherMass   surfaceGravity              public static void main String   args            if  args length    1                System err println  Usage  java Planet  lt earth weight gt                 System exit -1                     double earthWeight   Double parseDouble args 0            double mass   earthWeight EARTH surfaceGravity            for  Planet p   Planet values               System out printf  Your weight on  s is  f n                                p  p surfaceWeight mass              If you run Planet class from the command line with an argument of 175  you get this output        java Planet 175 Your weight on MERCURY is 66 107583 Your   weight on VENUS is 158 374842 Your weight on EARTH is   175 000000 Your weight on MARS is 66 279007 Your weight on JUPITER is 442 847567 Your weight on SATURN is 186 552719 Your   weight on URANUS is 158 397260 Your weight on NEPTUNE is   199 207413   Source  http   docs oracle com javase tutorial java javaOO enum html

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an Enum is a safe-type so you can t assign a new value at the runtime  Moreover you can use it in a switch statement  like an int

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An enumerated type is basically a data type that lets you describe each member of a type in a more readable and reliable way   Here is a simple example to explain why   Assuming you are writing a method that has something to do with seasons   The int enum pattern  First  you declared some int static constants to represent each season    public static final int SPRING   0  public static final int SUMMER   1  public static final int FALL   2  public static final int WINTER   2    Then  you declared a method to print name of the season into the console   public void printSeason int seasonCode        String name           if  seasonCode    SPRING            name    Spring             else if  seasonCode    SUMMER            name    Summer             else if  seasonCode    FALL            name    Fall             else if  seasonCode    WINTER            name    Winter             System out println  It is     name     now         So  after that  you can print a season name like this   printSeason SPRING   printSeason WINTER     This is a pretty common  but bad  way to do different things for different types of members in a class  However  since these code involves integers  so you can also call the method like this without any problems   printSeason 0   printSeason 1     or even like this  printSeason x - y   printSeason 10000     The compiler will not complain because these method calls are valid  and your printSeason method can still work    But something is not right here  What does a season code of 10000 supposed to mean  What if x - y results in a negative number  When your method receives an input that has no meaning and is not supposed to be there  your program knows nothing about it   You can fix this problem  for example  by adding an additional check       else if  seasonCode    WINTER        name    Winter     else       throw new IllegalArgumentException      System out println name     Now the program will throw a RunTimeException when the season code is invalid  However  you still need to decide how you are going to handle the exception   By the way  I am sure you noticed the code of FALL and WINTER are both 2  right    You should get the idea now  This pattern is brittle  It makes you write condition checks everywhere  If you re making a game  and you want to add an extra season into your imaginary world  this pattern will make you go though all the methods that do things by season  and in most case you will forget some of them   You might think class inheritance is a good idea for this case  But we just need some of them and no more   That s when enum comes into play     Use enum type  In Java  enum types are classes that export one instance for each enumeration constant via a public static final field   Here you can declare four enumeration constants  SPRING  SUMMER  FALL  WINTER  Each has its own name   public enum Season       SPRING  Spring    SUMMER  Summer    FALL  Fall    WINTER  Winter         private String name       Season String name            this name   name             public String getName             return name            Now  back to the method   public void printSeason Season season        System out println  It is     season getName       now         Instead of using int  you can now use Season as input  Instead of a condition check  you can tell Season to give you its name   This is how you use this method now   printSeason Season SPRING   printSeason Season WINTER   printSeason Season WHATEVER    lt -- compile error   You will get a compile-time error when you use an incorrect input  and you re guaranteed to get a non-null singleton reference of Season as long as the program compiles    When we need an additional season  we simply add another constant in Season and no more   public enum Season       SPRING  Spring    SUMMER  Summer    FALL  Fall    WINTER  Winter         MYSEASON  My Season             Whenever you need a fixed set of constants  enum can be a good choice  but not always   It s a more readable  more reliable and more powerful solution

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You use an enum instead of a class if the class should have a fixed enumerable number of instances   Examples    DayOfWeek  nbsp   7 instances   enum CardSuit nbsp  nbsp  nbsp  nbsp   4 instances   enum Singleton  nbsp   1 instance nbsp  nbsp  nbsp   enum Product nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   variable number of instances   class User nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   variable number of instances   class Date nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   variable number of instances   class

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Java programming language enums are far more powerful than their counterparts in other languages  which are little more than glorified integers  The new enum declaration defines a full-fledged class  dubbed an enum type   In addition to solving all the problems Not typesafe  No namespace  Brittleness and Printed values are uninformative  that exists with following int Enum pattern which was used prior to java 5 0    public static final int SEASON WINTER   0   it also allows you to add arbitrary methods and fields to an enum type  to implement arbitrary interfaces  and more  Enum types provide high-quality implementations of all the Object methods  They are Comparable and Serializable  and the serial form is designed to withstand arbitrary changes in the enum type  You can also use Enum in switch case   Read the full article on Java Enums http   docs oracle com javase 1 5 0 docs guide language enums html  for more details

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Enum serves as a type of fixed number of constants and can be used at least for two things  constant  public enum Month       JANUARY  FEBRUARY          This is much better than creating a bunch of integer constants   creating a singleton  public enum Singleton       INSTANCE        init      You can do quite interesting things with enums  look at here  Also look at the official documentation

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Enums are the recommended way to provide easy-to-remember names for a defined set of contants  optionally with some limited behaviour too     You should use enums where otherwise you would use multiple static integer constants  eg  public static int ROLE ADMIN   0 or BLOOD TYPE AB   2   The main advantages of using enums instead of these are type safety  compile type warnings errors when trying to use wrong values and providing a namespace for related  constants   Additionally they are easier to use within an IDE since it helps code completion too

[java] What's the use of "enum" in Java?

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