Hashtable vs Dictionary in C#: Understanding the Differences

Category > CSHARP || Published on : Friday, March 17, 2023 || Views: 253 || C# Hashtable Dictionary Data Structures Type Safety Performance


When working with key-value pairs in C#, developers often have to choose between using Hashtable or Dictionary. Both data structures are useful, but they have some key differences that can affect their suitability for specific use cases. In this article, we'll explore the differences between Hashtable and Dictionary in C# and discuss when to use each one. By the end of this article, you should have a clear understanding of how these two data structures differ and which one to choose for your project.

When it comes to storing key-value pairs in C#, developers often have to choose between Hashtable and Dictionary. While both data structures can store key-value pairs and have similar syntax, they have some key differences that make them better suited for different use cases.

Hashtable in C#

A Hashtable is a collection of key-value pairs that are stored in a hash table, which uses the hash code of the key to index and retrieve the value. This makes lookups fast, even for large collections. Hashtable is part of the System.Collections namespace and was introduced in .NET 1.0.

To create a Hashtable in C#, you can use the following code:

Hashtable myHashtable = new Hashtable();
myHashtable.Add("key1", "value1");
myHashtable.Add("key2", "value2");

In the above code, we create a new Hashtable instance and add two key-value pairs to it. The keys are strings ("key1" and "key2"), and the values are also strings ("value1" and "value2").

Dictionary in C#

A Dictionary is a generic collection of key-value pairs that are stored in a hash table. It's similar to Hashtable in many ways, but there are some key differences. Dictionary is part of the System.Collections.Generic namespace and was introduced in .NET 2.0.

To create a Dictionary in C#, you can use the following code:

Dictionary<string, string> myDictionary = new Dictionary<string, string>();
myDictionary.Add("key1", "value1");
myDictionary.Add("key2", "value2");

In the above code, we create a new Dictionary instance and add two key-value pairs to it. The keys and values are both strings, just like with Hashtable.

Differences between Hashtable and Dictionary

The key differences between Hashtable and Dictionary are as follows:

  1. Type safety: Hashtable is not type-safe, meaning that you can store any type of key or value in it. Dictionary, on the other hand, is type-safe and requires you to specify the types of the key and value when you create the instance.

  2. Performance: While both Hashtable and Dictionary use hash tables to store key-value pairs, Dictionary is generally faster because it's more optimized for modern CPUs and has better caching behavior.

  3. Null values: Hashtable allows null values for both keys and values, while Dictionary only allows null values for values.

Choosing between Hashtable and Dictionary

When choosing between Hashtable and Dictionary, consider the following factors:

  • If you need type safety, use Dictionary.
  • If performance is important and you don't need type safety, use Hashtable.
  • If you need to store null keys or null values, use Hashtable.

Conclusion

In summary, Hashtable and Dictionary are both useful data structures for storing key-value pairs in C#. Hashtable is older and less optimized, but it allows for null keys and values and is still useful in certain situations. Dictionary is faster and more type-safe, making it the preferred choice for most use cases. By understanding the differences between Hashtable and Dictionary, you can choose the one that best meets your needs.