C#中与Java的枚举相对应的是什么?
C#中与Java的枚举相对应的是什么?
在C#中并没有完全实现Java枚举的功能。但是,您可以通过使用嵌套类型和私有构造函数来接近这个功能。例如:
using System;
using System.Collections.Generic;
using System.Xml.Linq;
public abstract class Operator
{
public static readonly Operator Plus = new PlusOperator();
public static readonly Operator Minus =
new GenericOperator((x, y) => x - y);
public static readonly Operator Times =
new GenericOperator((x, y) => x * y);
public static readonly Operator Divide =
new GenericOperator((x, y) => x / y);
// Prevent other top-level types from instantiating
private Operator()
{
}
public abstract int Execute(int left, int right);
private class PlusOperator : Operator
{
public override int Execute(int left, int right)
{
return left + right;
}
}
private class GenericOperator : Operator
{
private readonly Func<int, int, int> op;
internal GenericOperator(Func<int, int, int> op)
{
this.op = op;
}
public override int Execute(int left, int right)
{
return op(left, right);
}
}
}
当然你不必使用嵌套类型,但它们提供了 Java 枚举所擅长的"自定义行为"部分。在其他情况下,您可以通过将参数传递给私有构造函数来获取一个众所周知的受限值集。
这里有一些它无法提供的东西:
EnumSet
虽然有些需要努力才能实现,但其中一些可能是可行的;尽管 Switch 没有黑科技不太现实。如果语言像这样做了一些事情,它可以通过自动进行黑科技来使 Switch 正常工作(例如,声明许多 const 字段并将任何枚举类型的 switch 更改为整数 switch,只允许“已知”情况。)
哦,而局部类型意味着您不必在同一个文件中拥有 所有 枚举值。如果每个值变得非常复杂(这绝对是可能的),每个值都可以有自己的文件。
private class GenericOperator : Operator
{
private readonly Func op;
internal GenericOperator(Func op)
{
this.op = op;
}
public override int Execute(int left, int right)
{
return op(left, right);
}
}
- Jonathan枚举类型是在Java中比C#更好实现的几个语言特性之一。
在Java中,枚举类型是完整的具名实例,并且属于一种类型,而C#枚举类型基本上是具有名称的常量。
尽管在基本情况下它们看起来相似,但是在Java中,您拥有更多的控制力,因为您可以向每个枚举添加行为,因为它们是完整的类。
您是否特别寻找某些功能?
这里有一个有趣的想法。我设计了以下枚举
基类:
public abstract class Enumeration<T>
where T : Enumeration<T>
{
protected static int nextOrdinal = 0;
protected static readonly Dictionary<int, Enumeration<T>> byOrdinal = new Dictionary<int, Enumeration<T>>();
protected static readonly Dictionary<string, Enumeration<T>> byName = new Dictionary<string, Enumeration<T>>();
protected readonly string name;
protected readonly int ordinal;
protected Enumeration(string name)
: this (name, nextOrdinal)
{
}
protected Enumeration(string name, int ordinal)
{
this.name = name;
this.ordinal = ordinal;
nextOrdinal = ordinal + 1;
byOrdinal.Add(ordinal, this);
byName.Add(name, this);
}
public override string ToString()
{
return name;
}
public string Name
{
get { return name; }
}
public static explicit operator int(Enumeration<T> obj)
{
return obj.ordinal;
}
public int Ordinal
{
get { return ordinal; }
}
}
它有一个类型参数,基本上是为了使不同派生枚举中的序数计数工作正常。Jon上面的Operator
示例变成:
public class Operator : Enumeration<Operator>
{
public static readonly Operator Plus = new Operator("Plus", (x, y) => x + y);
public static readonly Operator Minus = new Operator("Minus", (x, y) => x - y);
public static readonly Operator Times = new Operator("Times", (x, y) => x * y);
public static readonly Operator Divide = new Operator("Divide", (x, y) => x / y);
private readonly Func<int, int, int> op;
// Prevent other top-level types from instantiating
private Operator(string name, Func<int, int, int> op)
:base (name)
{
this.op = op;
}
public int Execute(int left, int right)
{
return op(left, right);
}
}
string
和int
,使得switch语句成为可能//Review the sample enum below for a template on how to implement a JavaEnum.
//There is also an EnumSet implementation below.
public abstract class JavaEnum : IComparable {
public static IEnumerable<JavaEnum> Values {
get {
throw new NotImplementedException("Enumeration missing");
}
}
public readonly string Name;
public JavaEnum(string name) {
this.Name = name;
}
public override string ToString() {
return base.ToString() + "." + Name.ToUpper();
}
public int CompareTo(object obj) {
if(obj is JavaEnum) {
return string.Compare(this.Name, ((JavaEnum)obj).Name);
} else {
throw new ArgumentException();
}
}
//Dictionary values are of type SortedSet<T>
private static Dictionary<Type, object> enumDictionary;
public static SortedSet<T> RetrieveEnumValues<T>() where T : JavaEnum {
if(enumDictionary == null) {
enumDictionary = new Dictionary<Type, object>();
}
object enums;
if(!enumDictionary.TryGetValue(typeof(T), out enums)) {
enums = new SortedSet<T>();
FieldInfo[] myFieldInfo = typeof(T).GetFields(BindingFlags.Static | BindingFlags.DeclaredOnly | BindingFlags.Public);
foreach(FieldInfo f in myFieldInfo) {
if(f.FieldType == typeof(T)) {
((SortedSet<T>)enums).Add((T)f.GetValue(null));
}
}
enumDictionary.Add(typeof(T), enums);
}
return (SortedSet<T>)enums;
}
}
//Sample JavaEnum
public class SampleEnum : JavaEnum {
//Enum values
public static readonly SampleEnum A = new SampleEnum("A", 1);
public static readonly SampleEnum B = new SampleEnum("B", 2);
public static readonly SampleEnum C = new SampleEnum("C", 3);
//Variables or Properties common to all enums of this type
public int int1;
public static int int2 = 4;
public static readonly int int3 = 9;
//The Values property must be replaced with a call to JavaEnum.generateEnumValues<MyEnumType>() to generate an IEnumerable set.
public static new IEnumerable<SampleEnum> Values {
get {
foreach(var e in JavaEnum.RetrieveEnumValues<SampleEnum>()) {
yield return e;
}
//If this enum should compose several enums, add them here
//foreach(var e in ChildSampleEnum.Values) {
// yield return e;
//}
}
}
public SampleEnum(string name, int int1)
: base(name) {
this.int1 = int1;
}
}
public class EnumSet<T> : SortedSet<T> where T : JavaEnum {
// Creates an enum set containing all of the elements in the specified element type.
public static EnumSet<T> AllOf(IEnumerable<T> values) {
EnumSet<T> returnSet = new EnumSet<T>();
foreach(T item in values) {
returnSet.Add(item);
}
return returnSet;
}
// Creates an enum set with the same element type as the specified enum set, initially containing all the elements of this type that are not contained in the specified set.
public static EnumSet<T> ComplementOf(IEnumerable<T> values, EnumSet<T> set) {
EnumSet<T> returnSet = new EnumSet<T>();
foreach(T item in values) {
if(!set.Contains(item)) {
returnSet.Add(item);
}
}
return returnSet;
}
// Creates an enum set initially containing all of the elements in the range defined by the two specified endpoints.
public static EnumSet<T> Range(IEnumerable<T> values, T from, T to) {
EnumSet<T> returnSet = new EnumSet<T>();
if(from == to) {
returnSet.Add(from);
return returnSet;
}
bool isFrom = false;
foreach(T item in values) {
if(isFrom) {
returnSet.Add(item);
if(item == to) {
return returnSet;
}
} else if(item == from) {
isFrom = true;
returnSet.Add(item);
}
}
throw new ArgumentException();
}
// Creates an enum set initially containing the specified element(s).
public static EnumSet<T> Of(params T[] setItems) {
EnumSet<T> returnSet = new EnumSet<T>();
foreach(T item in setItems) {
returnSet.Add(item);
}
return returnSet;
}
// Creates an empty enum set with the specified element type.
public static EnumSet<T> NoneOf() {
return new EnumSet<T>();
}
// Returns a copy of the set passed in.
public static EnumSet<T> CopyOf(EnumSet<T> set) {
EnumSet<T> returnSet = new EnumSet<T>();
returnSet.Add(set);
return returnSet;
}
// Adds a set to an existing set.
public void Add(EnumSet<T> enumSet) {
foreach(T item in enumSet) {
this.Add(item);
}
}
// Removes a set from an existing set.
public void Remove(EnumSet<T> enumSet) {
foreach(T item in enumSet) {
this.Remove(item);
}
}
}
枚举,或者你需要Java枚举拥有但C#没有的特定功能吗?