C# vs Java Enums: Which One Offers More Functionality?

C# vs Java Enums: A Comparison

Java enums offer a powerful way to define constants with additional functionality, such as constructors, methods, and instance variables. While C# enums may seem simpler at first glance, they have drawbacks compared to Java's robust implementation.

Key Differences

Feature	Java	C#
Constructors	Supported	Not supported
Methods	Supported	Requires extension methods
Instance variables	Supported	Requires custom attributes or dictionaries
Values	Immutable	Mutable

Overcoming the Differences

Extension Methods: To add functionality similar to Java enums, C# allows defining extension methods on enums. For example, the following code provides methods to calculate surface gravity and surface weight:

<code class="csharp">public static class Planets
{
    public static double GetSurfaceGravity(this Planet p) { /* ... */ }
    public static double GetSurfaceWeight(this Planet p, double otherMass) { /* ... */ }
}</code>

Custom Attributes: Custom attributes can be used to store additional information on enums. Here is a sample implementation:

<code class="csharp">[PlanetAttr(3.303e+23, 2.4397e6)]
public enum Planet
{
    MERCURY,
    VENUS,
    EARTH,
    // ...
}

public class PlanetAttr : Attribute
{
    public double Mass { get; private set; }
    public double Radius { get; private set; }

    public PlanetAttr(double mass, double radius)
    {
        Mass = mass;
        Radius = radius;
    }
}</code>

By accessing the custom attribute on an enum value, you can retrieve the associated properties.

Planet Enum Example

Here is a C# equivalent to Sun's Planet enum using extension methods and custom attributes:

<code class="csharp">public enum Planet
{
    [PlanetAttr(3.303e+23, 2.4397e6)] MERCURY,
    [PlanetAttr(4.869e+24, 6.0518e6)] VENUS,
    [PlanetAttr(5.976e+24, 6.37814e6)] EARTH,
    // ...
}

public static class Planets
{
    public const double G = 6.67300E-11;

    public static double GetSurfaceGravity(this Planet p)
    {
        PlanetAttr attr = GetAttr(p);
        return G * attr.Mass / (attr.Radius * attr.Radius);
    }

    public static double GetSurfaceWeight(this Planet p, double otherMass)
    {
        return otherMass * p.GetSurfaceGravity();
    }

    private static PlanetAttr GetAttr(Planet p)
    {
        FieldInfo field = typeof(Planet).GetField(Enum.GetName(typeof(Planet), p));
        return field.GetCustomAttribute<PlanetAttr>();
    }
}</code>

This code defines the Planet enum with custom attributes for mass and radius. The Planets class provides extension methods for calculating surface gravity and weight, which are accessible through the enums themselves.

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