In C#, non-generic collections are collections that can store elements of any data type. Here are some common non-generic collections in C#,
ArrayList
A dynamic array of objects that can be indexed, sorted, and searched. ArrayList automatically resizes as elements are added or removed, making it an efficient collection for changing data sets.
Stack
A last-in-first-out (LIFO) collection of objects that supports adding and removing elements at the top of the collection. A stack can be used to reverse the order of elements or to implement undo functionality in a program.
Queue
A first-in-first-out (FIFO) collection of objects that supports adding elements at the end and removing elements from the front. A queue can be used to implement a task queue or to implement a breadth-first search algorithm.
BitArray
A collection of bits that can be indexed, manipulated, and stored as a compact array of bits. BitArray can be used to represent a set of flags or to implement a compact representation of binary data.
Hashtable
A collection of key-value pairs that uses a hash code to quickly access elements based on the key. Hashtable is ideal for lookups where the key is used to index the data.
SortedList
A collection of key-value pairs that are sorted by key. SortedList can be used to implement a dictionary with a defined sort order, or to sort elements by key.
It's important to note that these collections are considered "non-generic" because they do not enforce strong typing on the elements stored in the collection. Elements stored in a non-generic collection must be cast to the appropriate type when they are retrieved from the collection. It is recommended to use generic collections instead of non-generic collections, as they offer improved type safety and performance.