哈希表

　  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]);
    }

  }

}