Queue Implementation in Java

A queue is a linear data structure which follows the FIFO (first-in first-out) principle. That means the object which is inserted first will be the first one out, followed by the object which was inserted next.

The queue supports below core operations –

  1. enqueue: Inserts an item at the rear of the queue.
  2. dequeue: Removes the object from the front of the queue thereby decremeting queue size by one.
  3. peek: Returns the object at the front of the queue without removing it.
  4. isEmpty: Tests if the queue is empty or not.
  5. size: Returns the number of elements present in the queue.

Below is the Queue implementation in Java using an array.


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Inserting 1
Inserting 2
Inserting 3
Front element is: 1
Removing 1
Front element is: 2
Queue size is 2
Removing 2
Removing 3
Queue Is Empty


The time complexity of enqueue(), dequeue(), peek(), isEmpty() and size() functions is constant. i.e. O(1).



Java’s library also contains a Queue interface that specifies queue operations. Below is an example of Queue interface using LinkedList implementation.


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Front element is: A
Front element is: C
Queue size is 2
Queue is not Empty

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Great. Thanks for the nice post.