public class BufferCorrect {
    private int cap, first, last;
    private Sema free, occupied;
    private Data[] a;
    public BufferCorrect(int n) {
        cap = n;
        first = last = 0;
        a = new Data[n];
        free = new Sema(n); 
        occupied = new Sema(0);
    }
    // Methoden sind nicht synchronized
    public void produce(Data d) throws 
                                InterruptedException {
        free.down();
        synchronized (this) {
            a[last] = d; last = (last+1) % cap;
        }
        occupied.up();
    }
    public Data consume() throws 
                          InterruptedException {
        Data result; occupied.down(); 
        synchronized (this) {
            result = a[first]; first = (first+1) % cap;
        }
        free.up(); return result;
    }
} // end of corrected class Buffer