Selecting a Collection Class

Be sure to choose your Collections class carefully. Using the wrong collection can restrict your use of the collection.

Consider the following questions:

• Do you need a sequential list where the element is typically discarded after its value is retrieved?
  • If yes, consider Queue orStack.
  • If not, consider the other collections.
• Do you need to access the elements in a certain order, such as first-in-first-out, last-in-first-out, or randomly?
  • Queue offers first-in-first-out access.
  • Stack offers last-in-first-out access.
  • The rest of the collections offer random access.
• Do you need to access each element by index?
  • ArrayList and StringCollection offer access to their elements by the zero-based index of the element.
  • Hashtable, SortedList, ListDictionary, and StringDictionary offer access to their elements by the key of the element.
  • NameObjectCollectionBase and NameValueCollection offer access to their elements by either the zero-based index or the key of the element.
• Will each element contain one value, a combination of one key and one value, or a combination of one key and multiple values?
  • One value: Use any of the collections based onIList.
  • One key and one value: Use any of the collections based on IDictionary.
  • One key and multiple values: Use the NameValueCollection class in the System.Collections.Specialized Namespace namespace.
• Do you need to sort the elements differently from how they were entered?
  • Hashtable sorts the elements by the hash code of the key.
  • SortedList sorts the elements by the key, based on an IComparer implementation.
  • ArrayList provides a Sort method that takes an IComparer implementation as a parameter.
• Do you need fast searches and retrieval of information?
  • ListDictionary is faster than Hashtable for small collections (10 items or less).
• Do you need collections that accept only strings?
  • StringCollection (based on IList) and StringDictionary (based on IDictionary) are in the System.Collections.Specialized namespace.

See Also

Creating and Manipulating Collections | System.Collections Namespace | System.Collections.Specialized Namespace