How Do C# and Java Enums Differ, and How Can We Bridge the Functionality Gap?

Differences between C# and Java enumerations and ways to bridge functional differences

Both Java and C# provide enumeration types, but there are significant differences in how they are implemented. Java enums are more powerful, while C# enums are relatively concise. This article explores these differences and shows how to emulate some of the functionality of Java enumerations in C#.

Differences in enumeration structures

Java enumerations are essentially classes, with instance members and methods. C# enumerations are value types, and their constants are not objects. Java enum constants are objects, while C# enum constants are just simple constants.

Functional differences

Java enums support method overloading and initializing constants with custom code. C# enums lack these capabilities.

Bridging functional differences

To make up for these shortcomings, C# provides extension methods. By defining extension methods on the enumeration type, we can simulate the missing functionality. Additionally, custom properties can complement method-like behavior by appending metadata to enumeration constants.

Simulating Java’s Planet enumeration in C#

To illustrate how to simulate Java's Planet enumeration in C#, we introduce extension methods to simulate the surfaceGravity() and surfaceWeight() methods:

public static class Planets
{
    public static double GetSurfaceGravity(this Planet p) => ...;
    public static double GetSurfaceWeight(this Planet p, double otherMass) => ...;
}

Additionally, we assign custom properties to each enum constant to populate the instance members:

[PlanetAttr(mass, radius)]
public enum Planet
{
    // 带有属性的枚举常量
}

class PlanetAttr : Attribute
{
    public double Mass { get; private set; }
    public double Radius { get; private set; }
    // 构造函数设置属性值
}

With this approach, C# provides a flexible workaround to cover the functionality of Java's enumeration implementation.

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