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copied!<p><strong><code>Dictionary</code></strong> <<<>>> <strong><code>Hashtable</code></strong> differences:</p> <ul> <li><strong>Generic</strong> <<<>>> <strong>Non-Generic</strong></li> <li>Needs <strong>own thread synchronization</strong> <<<>>> Offers <strong>thread safe</strong> version through <strong><code>Synchronized()</code></strong> method</li> <li>Enumerated item: <strong><code>KeyValuePair</code></strong> <<<>>> Enumerated item: <strong><code>DictionaryEntry</code></strong></li> <li>Newer (> <strong>.NET 2.0</strong>) <<<>>> Older (since <strong>.NET 1.0</strong>)</li> <li>is in <strong>System.Collections.Generic</strong> <<<>>> is in <strong>System.Collections</strong> </li> <li>Request to non-existing key <strong>throws exception</strong> <<<>>> Request to non-existing key <strong>returns null</strong></li> <li>potentially a bit <strong>faster for value types</strong> <<<>>> <strong>bit slower</strong> (needs boxing/unboxing) for value types</li> </ul> <p><strong><code>Dictionary</code></strong> / <strong><code>Hashtable</code></strong> similarities:</p> <ul> <li>Both are internally <strong>hashtables</strong> == fast access to many-item data according to key</li> <li>Both need <strong>immutable and unique keys</strong></li> <li>Keys of both need own <strong><code>GetHashCode()</code></strong> method</li> </ul> <p><strong>Similar</strong> .NET collections (candidates to use instead of Dictionary and Hashtable):</p> <ul> <li><code>ConcurrentDictionary</code> - <strong>thread safe</strong> (can be safely accessed from several threads concurrently)</li> <li><code>HybridDictionary</code> - <strong>optimized performance</strong> (for few items and also for many items)</li> <li><code>OrderedDictionary</code> - values can be <strong>accessed via int index</strong> (by order in which items were added)</li> <li><code>SortedDictionary</code> - items <strong>automatically sorted</strong></li> <li><code>StringDictionary</code> - strongly typed and <strong>optimized for strings</strong></li> </ul>

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