CareerCup

Circular queue using array:
Initialize head and tail to -1 and set buffer_size in the constructor
count is the variable to track the number of elements added to the queue. Since its shared by both enqueue and dequeue functions, we need to synchronize the methods to be thread safe.

public synchronized void enQueue(int item){
			if(count == buffer_size){
				System.out.println("Queue is full!!");
			}
			else{
				tail++;
				tail = tail % buffer_size;
				queueArray[tail] = item;
				count++;
			}
	}

Maybe we should acquire lock of queueArray[tail], not this, like in blocking queue. Because locking on this prevent any operations with queue.

Ya. We can use synchronize block instead. Like

synchronized (queueArray)
    {
       tail = tail++ % buffer_size;
	queueArray[tail] = item;
	count++;
  }

Obviously it is a blocking queue

public synchronized void enQueue(int item){
if(count == buffer_size){
wait();
}
else{
queueArray[tail] = item;
tail = tail++ % buffer_size;
count++;
notifyAll();
}
}

int front, rear;

public synchronized void enqueue(int A[], int x) {
	if (front == rear == -1) {
		A[front = rear = 0] = x;
	} else if ((rear + 1) % n != front) {
		A[rear = (rear + 1) % n] = x;
	} else {
		printf("Queue Overflowed!");
}