Dictionary VS Hashtable differences:

  • Generic <<<>>> Non-Generic
  • Needs own thread synchronization <<<>>> Offers thread safe version through Synchronized() method
  • Enumerated item: KeyValuePair <<<>>> Enumerated item: DictionaryEntry
  • Newer (> .NET 2.0) <<<>>> Older (since .NET 1.0)
  • is in System.Collections.Generic <<<>>> is in System.Collections
  • Request to non-existing key throws exception <<<>>> Request to non-existing key returns null
  • potentially a bit faster for value types <<<>>> bit slower (needs boxing/unboxing) for value types

Dictionary / Hashtable similarities:

  • Both are internally hashtables == fast access to many-item data according to key
  • Both need immutable and unique keys
  • Keys of both need own GetHashCode() method

Similar .NET collections (candidates to use instead of Dictionary and Hashtable):

  • ConcurrentDictionarythread safe (can be safely accessed from several threads concurrently)
  • HybridDictionaryoptimized performance (for few items and also for many items)
  • OrderedDictionary – values can be accessed via int index (by order in which items were added)
  • SortedDictionary – items automatically sorted
  • StringDictionary – strongly typed and optimized for strings

Source: http://stackoverflow.com/questions/301371/why-is-dictionary-preferred-over-hashtable

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