.NET HashTable Vs Dictionary - Can the Dictionary be as fast?

Jon_6486 0
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I am trying to figure out when and why to use a Dictionary or a HashTable. I have done a bit of a search on here and have found people talking about the generic advantages of the Dictionary which I totally agree with, which leads the boxing and unboxing advantage for a slight performance gain.

But I have also read the Dictionary will not always return the objects in the order they are inserted, thing it is sorted. Where as a HashTable will. As I understand it this leads to the HashTable being far faster for some situations.

My question is really, what might those situations be? Am I just wrong in my assumptions above? What situations might you use to choose one above the other, (yes the last one is a bit ambiguous).

dictionary collections hashtable .net c#
10 Answers

System.Collections.Generic.Dictionary<TKey, TValue> and System.Collections.Hashtable classes both maintain a hash table data structure internally. None of them guarantee preserving the order of items.

Leaving boxing/unboxing issues aside, most of the time, they should have very similar performance.

The primary structural difference between them is that Dictionary relies on chaining (maintaining a list of items for each hash table bucket) to resolve collisions whereas Hashtable uses rehashing for collision resolution (when a collision occurs, tries another hash function to map the key to a bucket).

There is little benefit to use Hashtable class if you are targeting for .NET Framework 2.0+. It's effectively rendered obsolete by Dictionary<TKey, TValue>.

user_337080

Another important difference is that the Hashtable type supports lock-free multiple readers and a single writer at the same time, while Dictionary does not.

user_2934670

Both are effectively the same class (you can look at the disassembly). HashTable was created first before .Net had generics. Dictionary, however is a generic class and gives you strong typing benefits. I would never use HashTable since Dictionary costs you nothing to use.

user_913610

Dictionaries have the advantage of being a generic type, which makes it type safe and a bit faster due to lack of need for boxing. The following comparison table (constructed using the answers found in a similar SO question post) illustrates some of the other reasons that support dictionaries over hash tables (or vice versa).

user_99155970

Dictionary is faster than hashtable as dictionary is a generic strong type. Hashtable is slower as it takes object as data type which leads to boxing and unboxing.

user_12708560
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