In the dequeue() function of Queue.java, we do not check if the queue is empty. If we dequeue an empty queue, we should also get an error. Implement the empty check feature for enqueue(int x). (Hint: Use System.err.println() to print the error message.)

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package ds;

public class Queue {

public int size;

public int[] array;

public int head;

public int tail;

public Queue() {

size = 0;

array = null;

head = 0;

tail = 0;

}

public Queue(int _size) {

size = _size;

array = new int[size];

head = 0;

tail = 0;

}

/*

* Implement the ENQUEUE(Q, x) function

*/

public boolean IsEmpty() {

return (head == 0 && tail == 0);

}

public void enqueue(int x) {

int no;

if (tail == array.length && head == 0)

System.out.println("queue is full");

else {

array[tail] = x;

tail++;

}

}

/*

* Implement the DEQUEUE(Q) function

*/

public int dequeue() {

int num = -1;

if (IsEmpty())

System.out.println("queue is empty");

else {

num = array[head];

head++;

}

return num;

}

/*

* Convert queue to string in the format of #size, head, tail, [#elements]

*/

public String toString() {

String str;

str = size + ", " + head + ", " + tail + ", [";

for (int i = head; i % size < tail; i++)

str += array[i] + ",";

str += "]";

return str;

}

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

Queue q;

q = new Queue(10);

for (int i = 0; i < 5; i++)

q.enqueue(i);

System.out.println(q.toString());

for (int i = 0; i < 2; i++)

q.dequeue();

System.out.println(q.toString());

}

}