Question

Program in Java

Create a queue class to store integers and implement following methods:

1- void enqueue(int num): This method will add an integer to the queue (end of the queue).

2- int dequeue(): This method will return the first item in the queue (First In First Out).

3- void display(): This method will display all items in the queue (First item will be displayed first).

4- Boolean isEmpty(): This method will check the queue and if it is empty, this will return true, otherwise false.

Answer 1

class Queue {
        private static int front=0, rear=0, capacity=50;
        private static int queue[]=new int[50];;
        // function to insert an element
        // at the rear of the queue
        void enqueue(int data) {
                // check queue is full or not
                if (capacity == rear) {
                        System.out.printf("\nQueue is full\n");
                        return;
                }

                // insert element at the rear
                else {
                        queue[rear] = data;
                        rear++;
                }
                return;
        }

        boolean isEmpty() {
                return (front == rear);
        }

        

        // function to delete an element
        // from the front of the queue
        void dequeue() {
                // if queue is empty
                if (front == rear) {
                        System.out.printf("\nQueue is empty\n");
                        return;
                }

                else {
                        for (int i = 0; i < rear - 1; i++) {
                                queue[i] = queue[i + 1];
                        }

                        // store 0 at rear indicating there's no element
                        if (rear < capacity)
                                queue[rear] = 0;

                        // decrement rear
                        rear--;
                }
                return;
        }

        public void display() {
                int i;

                for (i = front; i < rear; i++) {
                        System.out.print(queue[i] + " ");
                }
                System.out.println();
        }

}

public class TestQueue {

        public static void main(String ar[]) {
                Queue q = new Queue();

                // inserting elements in the queue
                System.out.println(q.isEmpty());
                q.enqueue(10);
                q.enqueue(20);
                q.enqueue(30);
                q.enqueue(40);
                q.enqueue(50);
                q.display();
                q.dequeue();
                q.dequeue();
                q.display();
                System.out.println(q.isEmpty());
        }
}

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