QUEUE

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    System.out.print("Enter the size:");
    n = scanner.nextInt();
    queue = new int[n];
    int ch;
    do {
        System.out.println("\nEnter your choice:\n 1.INSERT\n2.DELETE\n3.DISPLAY\n0.EXIT");
        ch = scanner.nextInt();
        switch (ch) {
            case 1:
                insert();
                break;
            case 2:
                deleted();
                break;
            case 3:
                display();
                break;
            default:
                System.out.println("enter valid option...");
                break;
        }
    } while (ch != 0);
}

static void insert() {
    Scanner scanner = new Scanner(System.in);
    int item;
    if (rear >= n - 1) {
        System.out.println("queue is overflow");
    } else {
        System.out.print("Enter element to be inserted: ");
        item = scanner.nextInt();
        rear = rear + 1;
        queue[rear] = item;
        if (front == -1) {
            front = 0;
        }
        System.out.println("Insertion done... & item inserted=" + item);
    }
}

static void deleted() {
    if (front == -1) {
        System.out.println("queue is underflow");
    } else {
        System.out.println("Item deleted..." + queue[front]);
        if (front == rear) {
            front = -1;
            rear = -1;
        } else {
            front = front + 1;
        }
    }
}

static void display() {
    if (front == -1) {
        System.out.println("queue is empty");
    } else {
        for (int i = front; i <= rear; i++) {
            System.out.println(queue[i]);
        }
    }
}