public class PoolWithWait {

    private final Queue<String> queue = new LinkedList<>();

    public PoolWithWait() {
        for (int i = 0; i < 2; i++) {
            queue.add("String"+i);
        }
    }

    public String barrowString() {
        synchronized(queue) {
            while(queue.size()==0) {
                try {
                    System.out.println("waiting... ["+Thread.currentThread().getName()+"]");
                    queue.wait();
                    if(queue.size()!=0) {
                        System.out.println("barrow element after waiting ["+Thread.currentThread().getName()+"]");
                        return queue.poll();
                    }
                } catch (InterruptedException e) {
                    System.out.println("thread interrupted");
                }
            }
            System.out.println("barrow element without waiting ["+Thread.currentThread().getName()+"]");
            return queue.poll();
        }
    }

    public void returnString(String poolElement) {
        synchronized (queue) {
            queue.add(poolElement);
            queue.notifyAll();
        }
    }
}