C# - Queue

 Queue is a special type of collection that stores the elements in FIFO style (First In First Out), exactly opposite of the Stack<T> collection. It contains the elements in the order they were added. C# includes generic Queue<T> and non-generic Queue collection. It is recommended to use the generic Queue<T> collection.

Queue<T> Characteristics

  • Queue<T> is FIFO (First In First Out) collection.
  • It comes under System.Collection.Generic namespace.
  • Queue<T> can contain elements of the specified type. It provides compile-time type checking and doesn't perform boxing-unboxing because it is generic.
  • Elements can be added using the Enqueue() method. Cannot use collection-initializer syntax.
  • Elements can be retrieved using the Dequeue() and the Peek() methods. It does not support an indexer.

The following figure illustrates the Queue collection:

C# queue

Creating a Queue

You can create an object of the Queue<T> by specifying a type parameter for the type of elements it can store. The following example creates and adds elements in the Queue<T> using the Enqueue() method. A Queue collection allows null (for reference types) and duplicate values.

Example: Create and Add Elements in the Queue
Queue<int> callerIds = new Queue<int>();
callerIds.Enqueue(1);
callerIds.Enqueue(2);
callerIds.Enqueue(3);
callerIds.Enqueue(4);

foreach(var id in callerIds)
    Console.Write(id); //prints 1234
Try it

Queue<T> Properties and Methods

PropertyUsage
CountReturns the total count of elements in the Queue.
MethodUsage
Enqueue(T)Adds an item into the queue.
DequeueReturns an item from the beginning of the queue and removes it from the queue.
Peek()Returns an first item from the queue without removing it.
Contains(T)Checks whether an item is in the queue or not
Clear()Removes all the items from the queue.

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