Using hash tables and dictionaries in C#

Hashtable

Hashtable class represents a collection of key-and-value pairs that are organized based on the hash code of the key. It uses the key to access the elements in the collection.

Some of the commonly used methods in Hashtable class are −

Sr.No.	Method & Description
1	public virtual void Add(object key, object value); Adds an element with the specified key and value into the Hashtable.
2	public virtual void Clear(); Removes all elements from the Hashtable.
3	public virtual bool ContainsKey(object key); Determines whether the Hashtable contains a specific key.
4	public virtual bool ContainsValue(object value); Determines whether the Hashtable contains a specific value.

The following is an example showing the usage of Hashtable class in C# −

Example

 Live Demo

using System;
using System.Collections;

namespace Demo {
   class Program {
      static void Main(string[] args) {
         Hashtable ht = new Hashtable();

         ht.Add("D01", "Finance");
         ht.Add("D02", "HR");
         ht.Add("D03", "Operations");

         if (ht.ContainsValue("Marketing")) {
            Console.WriteLine("This department name is already in the list");
         } else {
            ht.Add("D04", "Marketing");
         }

         ICollection key = ht.Keys;

         foreach (string k in key) {
            Console.WriteLine(k + ": " + ht[k]);
         }
         Console.ReadKey();
      }
   }
}

输出

D04: Marketing
D02: HR
D03: Operations
D01: Finance

字典

字典是C#中的键值对集合。Dictionaryb6842da76bed01162354d37c4f2d3464包含在System.Collection.Generics命名空间中。

以下是一些方法：

序号	方法及描述
1	Add 在字典中添加键值对
2	Clear() 移除所有的键和值
3	Remove 移除指定键的元素
4	ContainsKey 检查字典中是否存在指定的键
5	ContainsValue 检查字典中是否存在指定的键值
6	Count 计算键值对的数量
7	Clear 从字典中移除所有元素

让我们看看如何向字典中添加元素并显示数量：

示例

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {

      IDictionary <int, int> d = new Dictionary <int, int> ();
      d.Add(1,44);
      d.Add(2,34);
      d.Add(3,66);
      d.Add(4,47);
      d.Add(5,76);

      Console.WriteLine(d.Count);
   }
}

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