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C# includes specialized classes for storing a series of values or objects, which are called collections.
There are two types of collection types available in C#: non-generic collections and generic collections.
The System.Collections namespace contains non-generic collection types, and the System.Collections.Generic namespace includes generic collection types.
In most cases, it is recommended to use generic collections, as they execute faster than non-generic collections and also minimize exceptions by providing compile-time errors.
C# includes the following generic collection classes in the System.Collections.Generic namespace.
| Generic collections | Description |
|---|---|
| List<T> | Generic List<T> contains elements of a specified type. When you add elements to it, it will automatically grow. |
| Dictionary<TKey,TValue> | Dictionary<TKey,TValue> contains key-value pairs. |
| SortedList<TKey,TValue> | SortedList stores key-value pairs. By default, it automatically adds elements in ascending order of keys. |
| Queue<T> | Queue<T> stores values in a First In, First Out (FIFO) style. It maintains the order of values added. It provides an Enqueue() method to add values, as well as a Dequeue() method to retrieve values from the collection. |
| Stack<T> | Stack<T> stores values in Last In, First Out (LIFO) order. It provides a Push() method to add values, as well as Pop() and Peek() methods to retrieve values. |
| Hashset<T> | Hashset<T> contains non-repetitive elements. It eliminates duplicate elements. |
| Non-generic collections | Usage |
|---|---|
| ArrayList | ArrayList can store objects of any type, such as arrays. However, unlike arrays, you do not need to specify the size of ArrayList, as it will automatically grow. |
| SortedList | SortedList stores key-value pairs. By default, it automatically arranges elements in ascending order of keys. C# includes both generic and non-generic SortedList collections. |
| Stack | The Stack stores these values in a Last In, First Out (LIFO) manner. It provides a Push() method to add values, as well as Pop() and Peek() methods to retrieve values. C# includes both generic and non-generic stacks. |
| Queue | Queue stores values in a first-in-first-out (FIFO) manner. It maintains the order of the values added. It provides an Enqueue() method to add values and a Dequeue() method to retrieve values from the collection. C# includes both generic and non-generic queues. |
| Hashtable | Hashtable stores key-value pairs. It retrieves the value by comparing the hash value of the key. |
| BitArray | BitArray manages a compact array of bit values, represented by boolean values, where true means the bit is on(1) false means the bit is off. |
In the next chapter, let's see each type of collection.