C#中哈希表(HashTable)用法实例详解(添加/移除/判断/遍历/排序等)

using System.Collections;
using System.Collections.Generic;

//添加一个keyvalue键值对：
HashtableObject.Add(key,value);
//移除某个keyvalue键值对：
HashtableObject.Remove(key);
//移除所有元素：
HashtableObject.Clear();
// 判断是否包含特定键key：
HashtableObject.Contains(key);

using System;
using System.Collections; //file使用Hashtable时，必须引入这个命名空间
class Program
{
 public static void Main()
 {
   Hashtable ht = new Hashtable(); //创建一个Hashtable实例
   ht.Add("北京", "帝都"); //添加keyvalue键值对
   ht.Add("上海", "魔都");
   ht.Add("广州", "省会");
   ht.Add("深圳", "特区");
   string capital = (string)ht["北京"];
   Console.WriteLine(ht.Contains("上海")); //判断哈希表是否包含特定键,其返回值为true或false
   ht.Remove("深圳"); //移除一个keyvalue键值对
   ht.Clear(); //移除所有元素
 }
}

using System;
using System.Collections;
class Program
{
  static Hashtable GetHashtable()
  {
    Hashtable hashtable = new Hashtable();
    hashtable.Add("名字", "小丽");
    hashtable.Add("年龄", 22);
    return hashtable;
  }
  static void Main()
  {
    Hashtable hashtable = GetHashtable();
    string name = (string)hashtable["名字"];
    Console.WriteLine(name);
    int age = (int)hashtable["年龄"];
    Console.WriteLine(age);
  }
}

using System;
using System.Collections;
using System.IO;
class Program
{
  static void Main()
  {
  Hashtable hashtable = new Hashtable();
  hashtable.Add(100, "西安");
  // 能转换成功
  string value = hashtable[100] as string;
  if (value != null)
  {
    Console.WriteLine(value);
  }
  // 转换失败，获取的值为null，但不会抛出错误。
  StreamReader reader = hashtable[100] as StreamReader;
  if (reader == null)
  {
     Console.WriteLine("西安不是StreamReader型");
  }
  // 也可以直接获取object值，再做判断
  object value2 = hashtable[100];
  if (value2 is string)
  {
    Console.Write("这个是字符串型: ");
    Console.WriteLine(value2);
  }
  }
}

for(DictionaryEntry de in ht) //ht为一个Hashtable实例
{
  Console.WriteLine(de.Key); //de.Key对应于keyvalue键值对key
  Console.WriteLine(de.Value); //de.Key对应于keyvalue键值对value
}

foreach (int key in hashtable.Keys)
{
  Console.WriteLine(key);
}

foreach (string value in hashtable.Values)
{
  Console.WriteLine(value);
}

ArrayList akeys=new ArrayList(ht.Keys);
akeys.Sort(); //按字母顺序进行排序
foreach(string key in akeys)
{
  Console.WriteLine(key + ": " + ht[key]); //排序后输出
}

Stopwatch sw = new Stopwatch();
Hashtable hashtable = new Hashtable();
Dictionary<string, int> dictionary = new Dictionary<string, int>();
int countNum = 1000000;
sw.Start();
for (int i = 0; i < countNum; i++)
{
  hashtable.Add(i.ToString(), i);
}
sw.Stop();
Console.WriteLine(sw.ElapsedMilliseconds); //输出: 744
sw.Restart();
for (int i = 0; i < countNum; i++)
{
  dictionary.Add(i.ToString(), i);
}
sw.Stop();
Console.WriteLine(sw.ElapsedMilliseconds); //输出: 489
sw.Restart();
for (int i = 0; i < countNum; i++)
{
  hashtable.ContainsKey(i.ToString());
}
sw.Stop();
Console.WriteLine(sw.ElapsedMilliseconds); //输出: 245
sw.Restart();
for (int i = 0; i < countNum; i++)
{
  dictionary.ContainsKey(i.ToString());
}
sw.Stop();
Console.WriteLine(sw.ElapsedMilliseconds); //输出: 192