C#中的泛型怎么使用

[petit]

c#中的泛型怎么使用，比如Hashtable怎么支持泛型的？
在java中可以这样 Hashtable<String,String> = new
Hashtable(String,String);
C#中就不行，甚至是语法解析不了

[petit]

我写错了
java中是这样写的Hashtable<String, String> table = new Hashtable<String, String>();
在c#中这样写，行不通，应该怎么表达呢？

[petit]

to weisunding(鼎鼎)：这样写在java中可以，在c#中不行
to crossrowman(godi)：我想知道System.Collections.Hashtable 是否内置支持泛型
to Macosx(总算毕业了) ：正确的语法是什么呢？
to namhyuk(namhyuk) ： 您说的很清楚，但这不是我想问的问题

[Macosx]

using System;
using System.Collections.Generic;

public class Example
{
public static void Main()
{
// Create a new dictionary of strings, with integer keys.
Dictionary<int, string> d = new Dictionary<int, string>();

// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
d.Add(1, "a");
d.Add(3, "abc");
d.Add(7, "abcdefg");
d.Add(19, "abc");

// The Add method throws an exception if the new key is
// already in the dictionary.
try
{
d.Add(7, "xxx");
}
catch (ArgumentException ae)
{
Console.WriteLine("An element with Key = 7 already exists.");
}

// The Item property is another name for the indexer, so you
// can omit its name when accessing elements.
Console.WriteLine("For key = 19, value = {0}.", d[19]);

// The indexer can be used to change the value associated
// with a key.
d[19] = "abcdefghijklmnopqrs";
Console.WriteLine("For key = 19, value = {0}.", d[19]);

// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
d[11] = "abcdefghijk";

// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
Console.WriteLine("For key = 5, value = {0}.", d[5]);
}
catch (KeyNotFoundException knfe)
{
Console.WriteLine("Key = 5 is not found.");
}

// When a program often has to try keys that turn out not to
// be in the dictionary, TryGetValue is the most efficient
// way to retrieve values.
string value = "";
if (d.TryGetValue(5, out value))
{
Console.WriteLine("For key = 5, value = {0}.", value);
}
else
{
Console.WriteLine("Key = 5 is not found.");
}

// ContainsKey is not an efficient way to retrieve values,
// but it's a good way to test keys before inserting them.
if (!d.ContainsKey(5))
{
d.Add(5, "abcde");
Console.WriteLine("Value added for key = 5: {0}", d[5]);
}

// When you use foreach to enumerate dictionary elements,
// the elements are retreived as KeyValuePair objects.
Console.WriteLine();
foreach( KeyValuePair<int, string> kvp in d )
{
Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value);
}

// To get the values alone, use the Values property.
Console.WriteLine();
Dictionary<int, string>.ValueCollection dvc = d.Values;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
foreach( string s in dvc )
{
Console.WriteLine("Value = {0}", s);
}

}

}

/* This code example produces the following output:

An element with Key = 7 already exists.
For key = 19, value = abc.
For key = 19, value = abcdefghijklmnopqrs.
Key = 5 is not found.
Key = 5 is not found.
Value added for key = 5: abcde

Key = 1, Value = a
Key = 3, Value = abc
Key = 7, Value = abcdefg
Key = 19, Value = abcdefghijklmnopqrs
Key = 11, Value = abcdefghijk
Key = 5, Value = abcde

Value = a
Value = abc
Value = abcdefg
Value = abcdefghijklmnopqrs
Value = abcdefghijk
Value = abcde
*/

[petit]

请问 Macosx(总算毕业了) ：
在我vs.net 2003 中 没有using System.Collections.Generic;这个命名空间啊，你是用什么版本的？为什么我没有

[petit]

是不是C# 2.0?如果是在2003中怎么使用，是beta版吗/

[稍微有点无敌]

应该是在2.0里面，.net1.1不支持泛型的

[yellowhwb]

vs.net 2003不支持泛型，vs.net 2005（.net framework 2.0）才支持泛型！

[itmingong]

up

[petit]

现在2005还在beta中，等啊～～～。
其实vs.net 2005只是一个ide，c# 2.0 能通过什么方法在2003中使用？

[Macosx]

如果说vs.net 2005有点不准确 那就用.net framework 2.0吧
自己也可以写一个强类型的hashtable 但得加不少代码

[nik_Amis]

/[up]

[TechEye]

Hashtable<String,String> hash = new Hashtable(String,String)();
应该是这样形式

[crossrowman]

http://www.microsoft.com/china/msdn/library/langtool/vcsharp/csharpgenerics.mspx

[Macosx]

语法不一样

[namhyuk]

Hashtable table = new Hashtable();
table.Add("Sunday", "星期天");
table.Add("Monday", "星期一");
table.Add("Tuesday", "星期二");
...

string cnDay = (string)table["Tuesday"];

Items can also be added to a Hashtable using string indexes:
Hashtable table = new Hashtable();
table["Sunday"] = "星期天";
table["Monday"] = "星期一";
table["Tuesday"] = "星期二";
...

there's a difference between adding items with Add and adding them with indexers. Add throws an exception if the key you pass to it is already in the table. Indexers don't. They simply replace the old value with the new one.

[claus2001]

mark

[julong88]

mark

[foolnet]

http://www.microsoft.com/china/msdn/library/langtool/vcsharp/csharpgenerics.mspx

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