public synchronized void put(Object o) {

    while (buf.size()==MAX_SIZE) {

        wait(); // called if the buffer is full (try/catch removed for brevity)

    }

    buf.add(o);

    notify(); // called in case there are any getters or putters waiting

}

public synchronized Object get() {

    // Y: this is where C2 tries to acquire the lock (i.e. at the beginning of the method)

    while (buf.size()==0) {

        wait(); // called if the buffer is empty (try/catch removed for brevity)

        // X: this is where C1 tries to re-acquire the lock (see below)

    }

    Object o = buf.remove(0);

    notify(); // called if there are any getters or putters waiting

    return o;

}