Esa.java

/**
 * @author Feder1co 5oave
 */
class Schedulatore {
	private final int N;
	private String[] seq;
	private int corrente;
	private boolean fine;
	
	public Schedulatore(int num) {
		N = num;
		corrente = num;
		seq = new String[num];
		fine = false;
	}
	
	public synchronized void nuovaSequenza(String[] seq) {
		try {
			while (corrente != N) wait();
		} catch (InterruptedException ex) {}
		
		for (int i = 0; i < N; i++) this.seq[i] = seq[i];
		corrente = 0;
		notifyAll();
	}
	
	public synchronized void fineEsecuzione() {
		fine = true;
	}
	
	public synchronized void aspettaTurno(String nome) {
		try {
			while (corrente == N || !nome.equals(seq[corrente]))
				wait();
		} catch (InterruptedException ex) {}
	}
	
	public synchronized boolean prossimoTurno() {
		corrente++;
		notifyAll();
		return fine;
	}
}

Pesa.java

class SchedulerThread extends Thread {
	Schedulatore sc;
	public SchedulerThread(Schedulatore aSched) {
		sc = aSched;
//		System.out.println("scheduler  created");
	}
	public void run() {
		String s[] = new String[4];
		
//		System.out.println("scheduler: 1st schedule");
		s[0] = "paperino"; s[1] = "topolino"; s[2] = "pippo"; s[3] = "pluto";
		sc.nuovaSequenza(s);

//		System.out.println("scheduler: 2st schedule");
		s[0] = "topolino"; s[1] = "pluto"; s[2] = "pippo"; s[3] = "paperino";
		sc.nuovaSequenza(s);

//		System.out.println("scheduler: 3st schedule");
		s[0] = "pluto"; s[1] = "paperino"; s[2] = "pippo"; s[3] = "topolino";
		sc.nuovaSequenza(s);
		
		sc.fineEsecuzione();
	}
		
}
	
class WorkerThread extends Thread {
		Schedulatore sch;
		public WorkerThread(String name, Schedulatore aSched) {
			super(name);
			sch= aSched;
//			System.out.println(getName() + " created");
		}
		public void run() {
			while (true) {
				sch.aspettaTurno(getName());
				System.out.println(getName());
				try {
					sleep(200);
					} catch(InterruptedException e){}
				if (sch.prossimoTurno()) break;
			}
		}
		
	}

public class Pesa {
	
	public static void main(String[] args) throws InterruptedException {

		final int N = 4;
		String names[] = {"pippo", "pluto", "paperino", "topolino"};
		Schedulatore manager = new Schedulatore(N);
		
		Thread sched = new SchedulerThread(manager);
		sched.start();
		Thread workers[] = new Thread[N];
		for (int i = 0; i < N; i++) {
			workers[i] = new WorkerThread(names[i], manager);
			workers[i].start();
		}
	}	
}