LinearQueue.java

import java.util.Scanner;

class Queue {
    int[] queue;
    int front, rear, size;

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

    // Insert element
    void enqueue(int value) {
        if (rear == size - 1) {
            System.out.println("Queue Overflow");
            return;
        }
        if (front == -1)
            front = 0;
        queue[++rear] = value;
        System.out.println(value + " inserted");
    }

    // Delete element
    void dequeue() {
        if (front == -1 || front > rear) {
            System.out.println("Queue Underflow");
            return;
        }
        System.out.println(queue[front] + " deleted");
        front++;
        if (front > rear) {
            front = -1;
            rear = -1;
        }
    }

    // Display queue
    void display() {
        if (front == -1) {
            System.out.println("Queue is empty");
            return;
        }
        System.out.print("Queue: ");
        for (int i = front; i <= rear; i++) {
            System.out.print(queue[i] + " ");
        }
        System.out.println();
    }
}

public class LinearQueue {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter queue size: ");
        int n = sc.nextInt();

        Queue q = new Queue(n);

        System.out.println("\nSelect from the listed options-");

        while (true) {
            System.out.println("1. Insert");
            System.out.println("2. Delete");
            System.out.println("3. Display");
            System.out.println("4. Exit");

            System.out.print("Enter choice: ");
            int choice = sc.nextInt();

            switch (choice) {
                case 1:
                    System.out.print("Enter value: ");
                    q.enqueue(sc.nextInt());
                    break;
                case 2:
                    q.dequeue();
                    break;
                case 3:
                    q.display();
                    break;
                case 4:
                    System.out.println("Program ended.");
                    sc.close();
                    return;
                default:
                    System.out.println("Invalid choice");
            }
        }
    }
}