Question

We can use any of these (includes List, ArrayList, Dictionary, Hashtable, Stack, Queue) to hold value or hold reference to other objects as a collection.

But, my question is which one is used when?

Answer 1

Lists

Lists allow duplicate items, can be accessed by index, and support linear traversal.

• ArrayList – An array-based list that doesn’t support generic types. It does not enforce type safety and should generally be avoided.

• List – An array list that supports generic types and enforces type-safety. Since it is non-contiguous, it can grow in size without re-allocating memory for the entire list. This is the more commonly used list collection.

Hashes

Hashes are look-ups in which you give each item in a list a “key” which will be used to retrieve it later. Think of a hash like a table index where you can ask questions like “I’m going to find this object by this string value. Duplicate keys are not allowed.

• HashTable – A basic key-value-pair map that functions like an indexed list.

• Dictionary – A hashtable that supports generic types and enforces type-safety.

Queues

Queues control how items in a list are accessed. You typically push/pop records from a queue in a particular direction (from either the front or back). Not used for random access in the middle.

• Stack – A LIFO (last in, first out) list where you push/pop records on top of each other.

• Queue – A FIFO (first in, first out) list where you push records on top and pop them off the bottom.