Hashtable()为哈希表，可以在保存值的同时保存关键字，便于以后搜索，如存储美国州名的同时存储州的简写，如简写为"CA"　,州名为"California",其有Add,Clear,Clone,CopyTo,ContainsKey等方法：

/*  Example11_7.cs illustrates the use of the Hashtable methods*/using System;using System.Collections;class Example11_7{  public static void Main()  {    // create a Hashtable object    Hashtable myHashtable = new Hashtable();    // add elements containing US state abbreviations and state    // names to myHashtable using the Add() method    myHashtable.Add("AL", "Alabama");    myHashtable.Add("CA", "California");    myHashtable.Add("FL", "Florida");    myHashtable.Add("NY", "New York");    myHashtable.Add("WY", "Wyoming");    // display the keys for myHashtable using the Keys property    foreach (string myKey in myHashtable.Keys)    {      Console.WriteLine("myKey = " + myKey);    }    // display the values for myHashtable using the Values property    foreach(string myValue in myHashtable.Values)    {      Console.WriteLine("myValue = " + myValue);    }    // use the ContainsKey() method to check if myHashtable    // contains the key "FL"    if (myHashtable.ContainsKey("FL"))    {      Console.WriteLine("myHashtable contains the key FL");    }    // use the ContainsValue() method to check if myHashtable    // contains the value "Florida"    if (myHashtable.ContainsValue("Florida"))    {      Console.WriteLine("myHashtable contains the value Florida");    }    // use the Remove() method to remove FL from myHashtable    Console.WriteLine("Removing FL from myHashtable");    myHashtable.Remove("FL");    // get the number of elements in myHashtable using the Count    // property    int count = myHashtable.Count;    // copy the keys from myHashtable into an array using    // the CopyTo() method and then display the array contents    Console.WriteLine("Copying keys to myKeys array");    string[] myKeys = new string[count];    myHashtable.Keys.CopyTo(myKeys, 0);    for (int counter = 0; counter < myKeys.Length; counter++)    {      Console.WriteLine("myKeys[" + counter + "] = " +        myKeys[counter]);    }    // copy the values from myHashtable into an array using    // the CopyTo() method and then display the array contents    Console.WriteLine("Copying values to myValues array");    string[] myValues = new string[count];    myHashtable.Values.CopyTo(myValues, 0);    for (int counter = 0; counter < myValues.Length; counter++)    {      Console.WriteLine("myValues[" + counter + "] = " +        myValues[counter]);    }  }}