public class Monitor {

    private int[] _data;
    private int   _index;

    public Monitor(int capacity) {
        _data = new int[capacity];
        _index = 0;
    }

    public synchronized void add(int number) {
        // room for more data?
        while ( _index >= _data.length ) {
            try {
                wait();
            } catch (InterruptedException ie) { }
        }
        // add number and notify waiting threads
        _data[_index++] = number;
        notifyAll();
    }

    public synchronized int get() {
        // is data to retreive?
        while ( _index <= 0 ) {
            try {
                wait();
            } catch (InterruptedException ie) { }
        }
        // get number and notify waiting threads
        int out = _data[--_index];
        notifyAll();
        return out;
    }

}