Hashtable VS. Dictionary

The Hashtable and Dictionary classes in C# are both used for storing key-value pairs, but there are several differences between them in terms of functionality, performance, and usage.

Type Safety

The Dictionary class is type-safe, meaning that you specify the type of both the keys and values when declaring an instance of the Dictionary class. This allows the compiler to enforce type checking and provides better type safety. On the other hand, the Hashtable class is not type-safe and allows any object to be used as keys and values.

Dictionary<string, int> dictionary = new Dictionary<string, int>(); dictionary.Add("Apple", 10); dictionary.Add("Banana", 5); Hashtable hashtable = new Hashtable(); hashtable.Add("Apple", 10); hashtable.Add("Banana", 5);

Performance

The Dictionary class generally provides better performance compared to the Hashtable class. The Dictionary class is implemented as a generic collection and uses hashing and indexing techniques optimized for performance. It has better lookup and retrieval times, especially for large data sets. The Hashtable class, on the other hand, uses a hash table data structure with object-based keys, which can result in slower performance due to boxing and unboxing operations.

Dictionary<string, int> dictionary = new Dictionary<string, int>(); dictionary["Apple"] = 10; dictionary["Banana"] = 5; Hashtable hashtable = new Hashtable(); hashtable["Apple"] = 10; hashtable["Banana"] = 5;

Null Key and Value

The Dictionary class does not allow null keys or values. If you attempt to add a null key or value to a Dictionary, it will throw an exception. In contrast, the Hashtable class allows null keys and values.

Dictionary<string, int> dictionary = new Dictionary<string, int>(); dictionary.Add(null, 10); // Throws an ArgumentNullException Hashtable hashtable = new Hashtable(); hashtable.Add(null, 10); // Allowed

Enumeration

The Dictionary class provides the ability to iterate over its elements using the foreach loop and LINQ queries. It also supports LINQ extension methods for querying and manipulating data. The Hashtable class, however, does not support LINQ and requires manual enumeration using the foreach loop or other techniques.

Dictionary<string, int> dictionary = new Dictionary<string, int>(); // Add key-value pairs foreach (KeyValuePair<string, int> pair in dictionary) { // Access key-value pair } Hashtable hashtable = new Hashtable(); // Add key-value pairs foreach (DictionaryEntry entry in hashtable) { // Access key-value pair }

Conclusion

The Dictionary class is a more modern and type-safe alternative to the Hashtable class in C#. It provides better performance, type safety, and support for LINQ. However, if you require compatibility with legacy code or need to allow null keys or values, the Hashtable class can still be used.






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