Queue.java

import Exceptions.OverflowException;
import Exceptions.UnderflowException;

import java.util.Scanner;

public class Queue {
 private int[] queue;
 private int size;
 private int front;
 private int rear;

 public Queue() {
 queue = null;
 size = 0;
 front = rear = -1;
 }

 public Queue(int size) {
 this.size = size;
 front = rear = -1;
 queue = new int[size];
 }

 public static void main(String[] args) {
 int ch, x;
 Scanner sc = new Scanner(System.in);
 System.out.print("Enter the size of the queue : ");
 int n = sc.nextInt();
 Queue q = new Queue(n);

 loop:
 for (; ; ) {
 System.out.print("1. Enqueue\n" +
 "2. Dequeue\n" +
 "3. Display\n" +
 "0. Exit\n" +
 "Enter your choice : ");
 ch = sc.nextInt();
 switch (ch) {
 case 0:
 break loop;
 case 1:
 System.out.print("Enter the number you want to enqueue : ");
 x = sc.nextInt();
 try {
 q.enqueue(x);
 } catch (OverflowException e) {
 System.out.println(e.getMessage());
 }
 break;
 case 2:
 try {
 x = q.dequeue();
 System.out.println(x + " has been removed");
 } catch (UnderflowException e) {
 System.out.println(e.getMessage());
 }
 break;
 case 3:
 q.display();
 break;
 default:
 System.out.println("Dude, seriously?\nI'm sure you can do better than that.\nTry again.");
 }
 System.out.println();
 }
 }

 private boolean isFull() {
 return rear >= size - 1;
 }

 private boolean isEmpty() {
 return front > rear;
 }

 public void enqueue(int x) throws OverflowException {
 if (front == -1)
 ++front;
 if (!isFull())
 queue[++rear] = x;
 else
 throw new OverflowException("Queue is full. Unable to enqueue");
 }

 public int dequeue() throws UnderflowException {
 if (isEmpty()) {
 throw new UnderflowException("Queue is empty. Unable to dequeue");
 }
 return queue[front++];
 }

 public void display() {
 if (isEmpty()) {
 System.out.println("Queue is empty");
 return;
 }
 System.out.print("[");
 for (int i = front; i < rear; i++)
 System.out.print(queue[i] + ", ");
 System.out.println(queue[rear] + "]");
 }
}