Queues.java

class Queue {
    int maxSize;
    int[] arr;
    int front;
    int back;

    Queue(int size) {
        maxSize = size;
        arr = new int[maxSize];
        front = 0;
        back = -1;
    }

    void insert(int value) {
        if (back == maxSize - 1) return; // full
        arr[++back] = value;
    }

    void delete() {
        if (front > back) return; // empty
        front++;
    }

    void display() {
        if (front > back) {
            System.out.println("queue is empty");
            return;
        }
        for (int i = front; i <= back; i++) {
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    void getsize() {
        System.out.println(back - front + 1);
    }
}

public class Queues {
    public static void main(String[] args) {
        Queue q = new Queue(5);
        q.display();
        q.insert(5);
        q.insert(7);
        q.insert(12);
        q.display();
        q.delete();
        q.display();
        q.getsize(); // size
    }
}