C# in Depth

Generic collection classes in .NET 2.0101pattern for multithreading. This is not particularly hard to write, and third-partyimplementations are available, but having these classes directly available in the frameworkwould be more welcome.Next we’ll look at the generic versions of SortedList, which are similar enough tobe twins.3.5.4 SortedList and SortedDictionaryThe naming of SortedList has always bothered me. It feels more like a map or dictionarythan a list. You can access the elements by index as you can for other lists(although not with an indexer)—but you can also access the value of each element(which is a key/value pair) by key. The important part of SortedList is that when youenumerate it, the entries come out sorted by key. Indeed, a common way of usingSortedList is to access it as a map when writing to it, but then enumerate the entriesin order.There are two generic classes that map to the same sort of behavior: Sorted-List and SortedDictionary. (From here on I’ll justcall them SortedList and SortedDictionary to save space.) They’re very similarindeed—it’s mostly the performance that differs. SortedList uses less memory,but SortedDictionary is faster in the general case when it comes to adding entries.However, if you add them in the sort order of the keys to start with, SortedListwill be faster.NOTEA difference of limited benefit—SortedList allows you to find the index ofa particular key or value using IndexOfKey and IndexOfValue, and toremove an entry by index with RemoveAt. To retrieve an entry by index,however, you have to use the Keys or Values properties, which implementIList and IList, respectively. The nongeneric versionsupports more direct access, and a private method exists in the generic version,but it’s not much use while it’s private. SortedDictionary doesn’tsupport any of these operations.If you want to see either of these classes in action, use listing 3.1 as a good startingpoint. Just changing Dictionary to SortedDictionary or SortedList will ensure thatthe words are printed in alphabetical order, for example.Our final collection class is genuinely new, rather than a generic version of anexisting nongeneric type. It’s that staple of computer science courses everywhere: thelinked list.3.5.5 LinkedListI suspect you know what a linked list is. Instead of keeping an array that is quick toaccess but slow to insert into, a linked list stores its data by building up a chain ofnodes, each of which is linked to the next one. Doubly linked lists (likeLinkedList) store a link to the previous node as well as the next one, so you caneasily iterate backward as well as forward.Licensed to Rhona Hadida