C# Generic & Non-generic Collections
C# includes specialized classes that store series of values or objects are called collections.
There are two types of collections available in C#: non-generic collections and generic collections.
The System.Collections namespace contains the non-generic collection types and System.Collections.Generic namespace includes generic collection types.
In most cases, it is recommended to use the generic collections because they perform faster than non-generic collections and also minimize exceptions by giving compile-time errors.
Generic Collections
C# includes the following generic collection classes in the System.Collections.Generic namespace.
| Generic Collections | Description |
|---|---|
| List<T> | Generic List<T> contains elements of specified type. It grows automatically as you add elements in it. |
| Dictionary<TKey,TValue> | Dictionary<TKey,TValue> contains key-value pairs. |
| SortedList<TKey,TValue> | SortedList stores key and value pairs. It automatically adds the elements in ascending order of key by default. |
| Queue<T> | Queue<T> stores the values in FIFO style (First In First Out). It keeps the order in which the values were added. It provides an Enqueue() method to add values and a Dequeue() method to retrieve values from the collection. |
| Stack<T> | Stack<T> stores the values as LIFO (Last In First Out). It provides a Push() method to add a value and Pop() & Peek() methods to retrieve values. |
| Hashset<T> | Hashset<T> contains non-duplicate elements. It eliminates duplicate elements. |
Non-generic Collections
| Non-generic Collections | Usage |
|---|---|
| ArrayList | ArrayList stores objects of any type like an array. However, there is no need to specify the size of the ArrayList like with an array as it grows automatically. |
| SortedList | SortedList stores key and value pairs. It automatically arranges elements in ascending order of key by default. C# includes both, generic and non-generic SortedList collection. |
| Stack | Stack stores the values in LIFO style (Last In First Out). It provides a Push() method to add a value and Pop() & Peek() methods to retrieve values. C# includes both, generic and non-generic Stack. |
| Queue | Queue stores the values in FIFO style (First In First Out). It keeps the order in which the values were added. It provides an Enqueue() method to add values and a Dequeue() method to retrieve values from the collection. C# includes generic and non-generic Queue. |
| Hashtable | Hashtable stores key and value pairs. It retrieves the values by comparing the hash value of the keys. |
| BitArray | BitArray manages a compact array of bit values, which are represented as Booleans, where true indicates that the bit is on (1) and false indicates the bit is off (0). |
Let's see each type of collection next.