Queue implementation using an Array

Queue Implementation using Array

Last Updated: 16 November, 2024 🕓 4 Mins Read

A Queue is a linear data structure to store and manipulate the data elements. A queue follows the concept of "First in, First out" (FIFO), where the first element inserted into the queue is the first one to be deleted from the queue.

A queue is open at both ends which enables insert operations to be performed at one end called REAR or TAIL and delete operations to be performed at another end called FRONT or HEAD.

Operations in Queue:

Example: Queue Implementation using Array in Java

  class QueueImplUsingArray {
    int front, rear, array_size = 100;
    int[] queueArray;
  
    // Constructor to initialize the queue
    QueueImplUsingArray() {
      front = 0;
      rear = -1;
      queueArray = new int[array_size];
    }
  
    // Function to insert an element at the rear of the queue
    void enqueue(int data) {
      // Check if the queue is full
      if (rear == array_size - 1) {
        System.out.println("Queue is full");
        return;
      }
  
      // Insert element at the rear
      queueArray[++rear] = data;
    }
  
    // Function to delete an element from the front of the queue
    void dequeue() {
      // If the queue is empty
      if (front > rear) {
        System.out.println("Queue is empty");
        return;
      }
  
      // Shift all elements from index 1 till rear to the left by one
      for (int i = 0; i < rear; i++) {
        queueArray[i] = queueArray[i + 1];
      }
  
      // Decrement rear by 1
      rear--;
    }
  
    // Function to print all elements of queue
    void printQueue() {
      if (front > rear) {
        System.out.println("Queue is Empty");
        return;
      }
  
      // Traverse front to rear and print elements
      for (int i = front; i <= rear; i++) {
        System.out.print(queueArray[i] + "  ");
      }
      System.out.println(); // Line break
    }
  
    // Function to print the front of the queue
    void front() {
      if (rear == -1) {
        System.out.println("Queue is Empty");
        return;
      }
      System.out.println("Queue Front Element is: " + queueArray[front]);
    }
  
    public static void main(String[] args) {
      QueueImplUsingArray queue = new QueueImplUsingArray();
  
      // Print queue elements
      queue.printQueue();
  
      // Insert elements in the queue
      queue.enqueue(20);
      queue.enqueue(30);
      queue.enqueue(40);
      queue.enqueue(50);
  
      // Print queue elements
      queue.printQueue();
  
      // Insert element in the queue
      queue.enqueue(60);
  
      // Print queue elements
      queue.printQueue();
  
      // Dequeue elements
      queue.dequeue();
      queue.dequeue();
  
      System.out.print("Queue elements after two node deletions: ");
  
      // Print queue elements
      queue.printQueue();
  
      System.out.print("Queue elements after one insertion: ");
      queue.enqueue(60);
  
      // Print queue elements
      queue.printQueue();
  
      // Print front of the queue
      queue.front();
    }
  }