Insertion in a Queue in Java

class Queue {
    int front, rear, size;
    int capacity;
    int array[];
 
    public Queue(int capacity)
    {
        this.capacity = capacity;
        front = this.size = 0;
        rear = capacity - 1;
        array = new int[this.capacity];
    }
 
    // Queue is full when size becomes
    // equal to the capacity
    boolean isFull(Queue queue)
    {
        return (queue.size == queue.capacity);
    }
 
    // Queue is empty when size is 0
    boolean isEmpty(Queue queue)
    {
        return (queue.size == 0);
    }
 
    // Method to add an item to the queue.
    // It changes rear and size
    void enqueue(int item)
    {
        if (isFull(this))
            return;
        this.rear = (this.rear + 1)
                    % this.capacity;
        this.array[this.rear] = item;
        this.size = this.size + 1;
        System.out.println(item
                           + " enqueued to queue");
    }
 
 public void disp() /* function to display the elements of the queue */ {
	    
		System.out.print("\nThe elements in the queue are:");
		if(front == -1) {
			System.out.print("\nQueue is Empty");
		} 
                else {
			for(int i = front; i <= rear; i++) {
				System.out.print(array[i] + "  ");
			}
		}
		System.out.println();
	}
    
}
 
// Driver class
public class Main {
    public static void main(String[] args)
    {
        Queue queue = new Queue(1000);
 
        queue.enqueue(10);
        queue.enqueue(20);
        queue.enqueue(30);
        queue.enqueue(40);
        
        queue.disp();
 
        System.out.println();
 
        
    }
}