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社区首页 >问答首页 >C#与Java Enum (适用于C#新手)

C#与Java Enum (适用于C#新手)
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Stack Overflow用户
提问于 2009-01-22 14:19:13
回答 11查看 72.6K关注 0票数 193

我用Java语言编程已经有一段时间了,我刚刚进入了一个完全用C#编写的项目。我正在努力跟上C#的速度,并注意到我的新项目中有几个地方使用了枚举,但乍一看,C#的枚举似乎比1.5+实现更简单。有谁能列举出C#和Java枚举之间的差异,以及如何克服这些差异?(我不想引发一场语言火焰之战,我只想知道如何用C#做一些我过去用Java语言做的事情)。例如,有人能发布一个C#对应于Sun著名的Planet枚举示例吗?

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 ...]
EN

回答 11

Stack Overflow用户

回答已采纳

发布于 2009-01-22 14:25:03

CLR中的枚举是简单命名的常量。基础类型必须是整型的。在Java中,枚举更像是类型的命名实例。该类型可能非常复杂,并且-如您的示例所示-包含各种类型的多个字段。

为了将示例移植到C#,我只需将枚举更改为不可变的类,并公开该类的静态只读实例:

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;
    }
}
票数 226
EN

Stack Overflow用户

发布于 2011-01-24 11:30:49

在C#中,您可以在枚举上定义extension methods,这弥补了一些缺失的功能。

您可以将Planet定义为枚举,也可以使用与surfaceGravity()surfaceWeight()等效的扩展方法。

我已经按照Mikhail的建议使用了自定义属性,但使用字典也可以实现同样的效果。

using System;
using System.Reflection;

class PlanetAttr: Attribute
{
    internal PlanetAttr(double mass, double radius)
    {
        this.Mass = mass;
        this.Radius = radius;
    }
    public double Mass { get; private set; }
    public double Radius { get; private set; }
}

public static class Planets
{
    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();
    }

    public const double G = 6.67300E-11;

    private static PlanetAttr GetAttr(Planet p)
    {
        return (PlanetAttr)Attribute.GetCustomAttribute(ForValue(p), typeof(PlanetAttr));
    }

    private static MemberInfo ForValue(Planet p)
    {
        return typeof(Planet).GetField(Enum.GetName(typeof(Planet), p));
    }

}

public enum Planet
{
    [PlanetAttr(3.303e+23, 2.4397e6)]  MERCURY,
    [PlanetAttr(4.869e+24, 6.0518e6)]  VENUS,
    [PlanetAttr(5.976e+24, 6.37814e6)] EARTH,
    [PlanetAttr(6.421e+23, 3.3972e6)]  MARS,
    [PlanetAttr(1.9e+27,   7.1492e7)]  JUPITER,
    [PlanetAttr(5.688e+26, 6.0268e7)]  SATURN,
    [PlanetAttr(8.686e+25, 2.5559e7)]  URANUS,
    [PlanetAttr(1.024e+26, 2.4746e7)]  NEPTUNE,
    [PlanetAttr(1.27e+22,  1.137e6)]   PLUTO
}
票数 232
EN

Stack Overflow用户

发布于 2009-01-22 14:28:49

C#枚举实际上是完整的类,可以有私有的构造函数和方法等,而Java枚举只是命名为整数。IMO Java的实现要好得多。

This page should help you a lot while learning c# coming from a java camp. (链接指向枚举的区别(向上/向下滚动查看其他内容)

票数 13
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/469287

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