Data.java

public class Data {
    
    private int data;
    private boolean available = false;
    
    synchronized public void put(int value) {
        // there's already something in data
        while (available) {
            try {
                wait();
            } catch (InterruptedException e) { }
        }
        
        // nothing is available, should put something
        // and notify all threads that're waiting to regain the lock
        // and start execute their code again
        available = true;
        data = value;
        notifyAll();
    }
    
    synchronized public int get() {
        // there's nothing to get, go into a wait state until there'll be
        // something to consume
        while (!available) {
            try {
                wait();
            } catch (InterruptedException e) { }
        }
        
        available = false;
        notifyAll();
        
        return data;
    }
}