Queues Using Linked Lists

/*Copyrights to vsdevelopers.io*/
/*For more programs visit vsdevelopers.io */
/*Java program for queue operations using linked list*/
/*The operations are Insert,Delete, Search, Destroy*/
import java.util.Scanner;

public class VSDQueueList {
	static Scanner sc = new Scanner(System.in);

	// Class to hold the structure of nodes
	private static class VSDNode {
		int data;
		VSDNode next;
	}

	// Front end of queue
	static VSDNode front = null;
	// Rear end of queue
	static VSDNode rear = null;

	// Function to insert element onto the queue
	public static void VSDinsert() {
		System.out.println("Please Enter element to insert:");
		int element = sc.nextInt();
		VSDNode temp = new VSDNode();// making use of temporary node to insert
		temp.data = element;
		temp.next = null;
		if (front == null) {// Initially updating front and rear to the first element inserted
			front = temp;
			rear = temp;
		} else {// Inserting element and updating rear
			rear.next = temp;
			rear = temp;
		}
		VSDprintQueue();
	}

	// Function to delete element from the queue
	public static void VSDdelete() {

		if (rear == null) {// Checking whether the queue is empty
			System.out.println("Queue is empty!!");
		} else {
			int element = front.data;
			front = front.next;// Deleting element at front and updating front
			System.out.println("The deleted element is:" + element);
		}

	}

	// Function to search element in the queue
	public static void VSDsearch() {
		if (rear == null) {// Checking whether the queue is empty
			System.out.println("Queue is empty!!, Insert elements to search");
		}

		else {
			VSDNode temp = front;
			int flag = 0;// For marking presence of elements

			// Looping through out the list to find the element
			System.out.println("Please Enter element to serach:");
			int element = sc.nextInt();
			while (temp != null) {
				if (temp.data == element) {
					System.out.println("Element is present in the queue");
					flag = 1;
					break;
				}
				temp = temp.next;
			}
			if (flag == 0) {
				System.out.println("Element is not present in the queue");
			}

		}
	}

	// Function to destroy queue
	public static void VSDdestroy() {
		front = null;
		rear = null;
		System.out.println("Queue is destroyed");
	}

	// Function to print the Queue
	public static void VSDprintQueue() {
		System.out.println("Now the queue is");
		if (rear == null)
			System.out.println("Queue is Empty!!!");

		VSDNode temp = front;
		while (temp != null) {
			System.out.println(temp.data);
			temp = temp.next;
		}

	}

	public static void VSDuserInput() {
		System.out.println("Please Enter queue operation from:");
		System.out.println("Insert Delete Search Destroy");
		String choice = sc.next();
		switch (choice) {
		case "Insert":
		case "insert":
			VSDinsert();
			break;
		case "Delete":
		case "delete":
			VSDdelete();
			break;
		case "Search":
		case "search":
			VSDsearch();
			break;
		case "Destroy":
		case "destroy":
			VSDdestroy();
			break;
		}
		VSDuserChoice();
	}

	public static void VSDuserChoice() {
		System.out.println("For performing operations enter y else enter n");
		char ch = sc.next().charAt(0);
		if (ch == 'Y' || ch == 'y')
			VSDuserInput();
		else
			return;
	}

	public static void main(String args[]) {
		VSDuserInput();// Taking user input to perform queue operations
	}
}