Selecting a Collection Class

Be sure to choose your System.Collections class carefully. Using the wrong type 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 using the Queue<T> generic class if you need first-in-first-out (FIFO) behavior. Consider using the Stack<T> generic class if you need last-in-first-out (LIFO) behavior.

  • If not, consider using the other collections.

• Do you need to access the elements in a certain order, such as FIFO, LIFO, or random?

  • The Queue<T> generic class offer FIFO access.

  • The Stack<T> generic class offer LIFO access.

  • The LinkedList<T> generic class allows sequential access either from the head to the tail or from the tail to the head.

  • The rest of the collections offer random access.

• Do you need to access each element by index?

  • The List<T> generic class offers access to zero elements by the zero-based index of the element.

  • The Dictionary<TKey, TValue> generic class offers access to its elements by the key of the element.

  • The KeyedCollection<TKey, TItem> generic class offers access to its 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 on the IList interface or the IList<T> generic interface.

  • One key and one value: Use any of the collections based on the IDictionary interface or the IDictionary<TKey, TValue> generic interface.

  • One value with embedded key: Use the KeyedCollection<TKey, TItem> generic class.

• Do you need collections that accept only strings?

  • You can use any of the generic collection classes in the System.Collections.Generic namespace as strongly typed string collections by specifying the String class for their generic type arguments.