Question

I’ve been programming in Java for a while and just got thrown onto a project that’s written entirely in C#. I’m trying to come up to speed in C#, and noticed enums used in several places in my new project, but at first glance, C#’s enums seem to be more simplistic than the Java 1.5+ implementation. Can anyone enumerate the differences between C# and Java enums, and how to overcome the differences? (I don’t want to start a language flame war, I just want to know how to do some things in C# that I used to do in Java). For example, could someone post a C# counterpart to Sun’s famous Planet enum example?

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),   PLUTO   (1.27e+22,  1.137e6);    private final double mass;   // in kilograms   private final double radius; // in meters   Planet(double mass, double radius) {       this.mass = mass;       this.radius = radius;   }   public double mass()   { return mass; }   public double radius() { return radius; }    // universal gravitational constant  (m3 kg-1 s-2)   public static final double G = 6.67300E-11;    public double surfaceGravity() {       return G * mass / (radius * radius);   }   public double surfaceWeight(double otherMass) {       return otherMass * surfaceGravity();   } }  // Example usage (slight modification of Sun's example): public static void main(String[] args) {     Planet pEarth = Planet.EARTH;     double earthRadius = pEarth.radius(); // Just threw it in to show usage      // Argument passed in is earth Weight.  Calculate weight on each planet:     double earthWeight = Double.parseDouble(args[0]);     double mass = earthWeight/pEarth.surfaceGravity();     for (Planet p : Planet.values())        System.out.printf('Your weight on %s is %f%n',                          p, p.surfaceWeight(mass)); }  // Example output: $ java Planet 175 Your weight on MERCURY is 66.107583 Your weight on VENUS is 158.374842 [etc ...] 

Answer 1

Enumerations in the CLR are simply named constants. The underlying type must be integral. In Java an enumeration is more like a named instance of a type. That type can be quite complex and – as your example shows – contain multiple fields of various types.

To port the example to C# I would just change the enum to an immutable class and expose static readonly instances of that class:

using System; using System.Collections.Generic;  namespace ConsoleApplication1 {     class Program     {         static void Main(string[] args)         {             Planet planetEarth = Planet.MERCURY;              double earthRadius = pEarth.Radius; // Just threw it in to show usage             double earthWeight = double.Parse('123');             double earthMass   = earthWeight / pEarth.SurfaceGravity();              foreach (Planet p in Planet.Values)                 Console.WriteLine($'Your weight on {p} is {p.SurfaceWeight(mass)}');              Console.ReadKey();         }     }      public class Planet     {         public static readonly Planet MERCURY = new Planet('Mercury', 3.303e+23, 2.4397e6);         public static readonly Planet VENUS   = new Planet('Venus', 4.869e+24, 6.0518e6);         public static readonly Planet EARTH   = new Planet('Earth', 5.976e+24, 6.37814e6);         public static readonly Planet MARS    = new Planet('Mars', 6.421e+23, 3.3972e6);         public static readonly Planet JUPITER = new Planet('Jupiter', 1.9e+27, 7.1492e7);         public static readonly Planet SATURN  = new Planet('Saturn', 5.688e+26, 6.0268e7);         public static readonly Planet URANUS  = new Planet('Uranus', 8.686e+25, 2.5559e7);         public static readonly Planet NEPTUNE = new Planet('Neptune', 1.024e+26, 2.4746e7);         public static readonly Planet PLUTO   = new Planet('Pluto', 1.27e+22, 1.137e6);          public static IEnumerable<Planet> Values         {             get             {                 yield return MERCURY;                 yield return VENUS;                 yield return EARTH;                 yield return MARS;                 yield return JUPITER;                 yield return SATURN;                 yield return URANUS;                 yield return NEPTUNE;                 yield return PLUTO;             }         }          public string Name   { get; private set; }         public double Mass   { get; private set; }         public double Radius { get; private set; }          Planet(string name, double mass, double radius) =>              (Name, Mass, Radius) = (name, mass, radius);          // Wniversal gravitational constant  (m3 kg-1 s-2)         public const double G = 6.67300E-11;         public double SurfaceGravity()            => G * mass / (radius * radius);         public double SurfaceWeight(double other) => other * SurfaceGravity();         public override string ToString()         => name;     } }