我已经用Java编程了一段时间,只是被扔到一个完全用C#编写的项目中。我试图提高C#的速度,并注意到在我的新项目中的多个地方都使用了枚举,但是乍一看,C#的枚举似乎比Java 1.5+实现更简单。谁能列举C#和Java枚举之间的差异,以及如何克服这些差异?(我不想发动语言大战,我只想知道如何用Java来做C#中的某些事情)。例如,有人可以在Sun著名的Planet枚举示例中发布C#副本吗?
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 ...]
CLR中的枚举简称为常量。基础类型必须是整数。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-包含多个不同类型的字段。
要将示例移植到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; } }