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

Asked 2012-04-02T00:45:37.263
194

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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2 Answers

7

enum Benefits:

  1. Enums are type-safe, static fields are not
  2. 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)
  3. 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)

"such as the ability to easily assign an enum element a certain value"

enum EnumX{
  VAL_1(1),
  VAL_200(200);
  public final int certainValue;
  private X(int certainValue){this.certainValue = certainValue;}
}

"and consequently the ability to convert an integer to an enum without a decent amount of effort" Add a method converting int to enum which does that. Just add static HashMap<Integer, EnumX> containing the mapping.

If you really want to convert ord=VAL_200.ordinal() back to val_200 just use: EnumX.values()[ord]

answered 2012-04-02T01:58:40.927
6

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.
answered 2012-04-02T07:21:23.990

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