Queue Implementation Using Arrays.

Main.java

public class Main {
    
    public static void main(String[] args) {
        QueueUsingArray queue = new QueueUsingArray();
        System.out.println(queue.isFull()?"Full":"Not Full");
        System.out.println(queue.isEmpty()?"Empty":"Not Empty");

        queue.enQueue(11);
        queue.enQueue(101);
        queue.enQueue(1111);

        System.out.println("Peek at 2 " + queue.peek(2));
        
        queue.enQueue(1221);
        
        System.out.println("Elements");
        queue.printQueue();
        System.out.println(queue.isEmpty()?"Empty":"Not Empty");

        queue.deQueue();
        queue.deQueue();
        queue.deQueue();
        System.out.println("Elements");
        queue.printQueue();

        System.out.println("Peek at 2 "+ queue.peek(1));
        System.out.println(queue.isFull()?"Full":"Not Full");
        queue.deQueue();
        queue.deQueue();
        System.out.println(queue.isFull()?"Full":"Not Full");

    }

}

QueueUsingArray.java

// Queue Implementation Using Arrays
class QueueUsingArray {

    private int size = 10;
    private Object[] queue = new Object[size];
    private int frontIndex = 0;
    private int rearIndex = 0;

    public void enQueue(Object element) {
        if (isFull()) {
            System.out.println("Queue is full.");
        } else {
            queue[rearIndex] = element;
            rearIndex++;
        }
    }

    public Object deQueue() {
        if (isEmpty()) {
            System.out.println("Queue is empty.");
            return -1;
        } else {
            Object obj = queue[frontIndex];
            queue[frontIndex] = 0;
            frontIndex++;
            return obj;
        }
    }

    public Object peek(int position) {
        if (queue[position] == null) {
            System.out.print("No Element At " + position + " ");
            return -1;
        } else {
            if (position == frontIndex)
                return queue[position];
            else {
                return queue[frontIndex + position - 1];
            }
        }
    }

    public Object getFirst() {
        return queue[frontIndex];
    }

    public Object getLast() {
        return queue[rearIndex];
    }

    public boolean isEmpty() {
        return rearIndex <= 0;
    }

    public boolean isFull() {
        return rearIndex + 1 == size;
    }

    public void printQueue() {
        for (int index = frontIndex; index < rearIndex; index++) {
            System.out.print(queue[index] + " ");
        }
        System.out.println();
    }

}