C#中Hashtable和Dictionary的区别

在 C# 中，Dictionary 是一个泛型集合，通常用于存储键/值对。字典在System.Collection.Generics命名空间下定义。它本质上是动态的，这意味着字典的大小会根据需要增加。

例子：

// C# program to illustrate Dictionary
using System;
using System.Collections.Generic;
  
class GFG {
  
    // Main Method
    static public void Main()
    {
  
        // Creating a dictionary
        // using Dictionary class
        Dictionary My_dict = 
                    new Dictionary();
  
        // Adding key/value pairs in the Dictionary
        // Using Add() method
        My_dict.Add("a.01", "C");
        My_dict.Add("a.02", "C++");
        My_dict.Add("a.03", "C#");
  
        foreach(KeyValuePair element in My_dict)
        {
            Console.WriteLine("Key:- {0} and Value:- {1}", 
                              element.Key, element.Value);
        }
    }
}

输出：

Key:- a.01 and Value:- C
Key:- a.02 and Value:- C++
Key:- a.03 and Value:- C#

Hashtable 是基于键的哈希码排列的键/值对的集合。或者换句话说，哈希表用于创建使用哈希表进行存储的集合。它是在 System.Collections命名空间中定义的非泛型集合类型。在 Hashtable 中，key 对象必须是不可变的，只要它们在 Hashtable 中用作 key。

例子：

// C# program to illustrate a hashtable
using System;
using System.Collections;
  
class GFG {
  
    // Main method
    static public void Main()
    {
  
        // Create a hashtable
        // Using Hashtable class
        Hashtable my_hashtable = new Hashtable();
  
        // Adding key/value pair in the hashtable
        // Using Add() method
        my_hashtable.Add("A1", "Welcome");
        my_hashtable.Add("A2", "to");
        my_hashtable.Add("A3", "GeeksforGeeks");
  
        foreach(DictionaryEntry element in my_hashtable)
        {
            Console.WriteLine("Key:- {0} and Value:- {1} ",
                               element.Key, element.Value);
        }
    }
}

输出：

Key:- A3 and Value:- GeeksforGeeks 
Key:- A2 and Value:- to 
Key:- A1 and Value:- Welcome 

哈希表与字典

Hashtable	Dictionary
A Hashtable is a non-generic collection.	A Dictionary is a generic collection.
Hashtable is defined under System.Collections namespace.	Dictionary is defined under System.Collections.Generic namespace.
In Hashtable, you can store key/value pairs of the same type or of the different type.	In Dictionary, you can store key/value pairs of same type.
In Hashtable, there is no need to specify the type of the key and value.	In Dictionary, you must specify the type of key and value.
The data retrieval is slower than Dictionary due to boxing/ unboxing.	The data retrieval is faster than Hashtable due to no boxing/ unboxing.
In Hashtable, if you try to access a key that doesn’t present in the given Hashtable, then it will give null values.	In Dictionary, if you try to access a key that doesn’t present in the given Dictionary, then it will give error.
It is thread safe.	It is also thread safe but only for public static members.
It doesn’t maintain the order of stored values.	It always maintain the order of stored values.