In providing services in computer science, transport, and operations research a queue is a buffer where various entities such as data, objects, persons, or events are stored and waiting to be processed. The most well known operation of the queue is the First-In-First-Out (FIFO) queue process — In a FIFO queue, the first element in the queue will be the first one out; this is equivalent to the requirement that whenever an element is added, all elements that were added before have to be removed before the new element can be invoked. There are two basic operations associated with a queue: enqueue and dequeue. Enqueue means adding a new item to the rear of the queue while dequeue refers to removing the front item from queue and returns it in item. Following code shows how to implement a queue using arrays.

Array Implementation of Queue. Up vote 7 down vote favorite. I've implemented the queue data structures using array in java. Implement data structure overflow. Java Program To Implement Circular Queue Adt Using An Array In Excel Chapter 1. 6: Queues and Priority Queues. This chapter presents two.

The queue is one of the most widely used data structures. So what are queues? Where are they used?

How are they implemented? The Basics A queue is a FIFO sequence. Addition takes place only at the tail, and removal takes place only at the head. The basic operations are: • enqueue(x): add an item at the tail • dequeue: remove the item at the head • peek: return the item at the head (without removing it) • size: return the number of items in the queue • isEmpty: return whether the queue has no items Usage You tend to see queues often. Exercise: Draw a series of pictures that trace the execution of the following code fragment: Queue q = new BoundedQueue(4); q.enqueue('A'); q.enqueue('B'); q.enqueue('C'); q.dequeue(); q.enqueue('D'); q.dequeue(); q.enqueue('E'); q.enqueue('F'); A Linked Implementation This particular version uses dual head and tail pointers. Note here: • Adding to an empty queue is a little different than adding to a queue that already has elements, because we have to update the head in the former case but not the latter.

• Removal has three distinct cases: removing from a queue with more than one element, removing the last element, and removing from an empty queue. Exercise: Draw a class diagram for the interface and three implementing classes above.

Unit Testing Here is what we need to test: • A queue is empty on construction • A queue has size 0 on construction • After n enqueues to an empty queue, n >0, the queue is not empty and its size is n • If one enqueues x then dequeues, the value dequeued is x. • If one enqueues x then peeks, the value returned is x, but the size stays the same • If the size is n, then after n dequeues, the stack is empty and has a size 0 • If one enqueues the values 1 through 50, in order, into an empty queue, then if 50 dequeues are done the values dequeues are 1 through 50. • Dequeueing from an empty queue does throw a NoSuchElementException • Peeking into an empty queue does throw a NoSuchElementException • For bounded queues only, pushing onto a full stack does throw an IllegalStateException We really have three classes to test, but the test cases share a bunch of things in common; the common tests can go in a base class. Note how the base test class tests any kind of queue.