package jtp;

public class Seat {

    private boolean occupied;

    public Seat(Boolean occupied) {
        this.occupied = occupied;
    }

    public boolean isOccupied() {
        return occupied;
    }
}

------------------------------------------------------

package jtp;

import java.util.ArrayList;

public class Waggon {

    ArrayList<Seat> seats;

    public Waggon(ArrayList<Seat> seats) {
        this.seats = seats;
    }

    public ArrayList<Seat> getSeats() {
        return seats;
    }
}

------------------------------------------------------

package jtp;

import java.util.ArrayList;

public class Train {

    private ArrayList<Waggon> waggons;

    public Train(ArrayList<Waggon> waggons) {

        this.waggons = waggons;
    }

    public ArrayList<Seat> freeSeats() throws NoWaggons, NoSeats {

        ArrayList<Seat> free = new ArrayList<>();

        if (waggons.isEmpty()) throw new NoWaggons("Nie ma wagonow");

        for (Waggon waggon: waggons) {

            if (waggon.getSeats().isEmpty()) throw new NoSeats("Nie ma miejsc");

            for (Seat seat: waggon.getSeats()) {

                if (!seat.isOccupied()) {

                    free.add(seat);
                }
            }

        }

        return free;
    }
}

--------------------------------------------------------------------

package jtp;

public class NoSeats extends Exception {

    public NoSeats(String message) {
        super(message);
    }
}

---------------------------------------------------------------------

package jtp;

public class NoWaggons extends Exception{

    public NoWaggons(String message) {
        super(message);
    }
}

--------------------------------------------------------------------

package jtp;

import java.util.ArrayList;

public class Main {

    public static void main(String[] args) {

        ArrayList<Seat> tmpSeat = new ArrayList<>();

        for (int i = 0; i < 10; i++) {

            if (i % 2 == 0) {

                tmpSeat.add(new Seat(false));
            }

            else {

                tmpSeat.add(new Seat(true));
            }
        }

        ArrayList<Waggon> tmpWaggon = new ArrayList<>();
        tmpWaggon.add(new Waggon(tmpSeat));

        Train train = new Train(tmpWaggon);

        try {

            ArrayList<Seat> tmpFreeSeats = train.freeSeats();

            for (Seat seat: tmpFreeSeats) {

                System.out.println(seat.isOccupied());
            }
        }
        catch (NoWaggons | NoSeats e) {

            e.getMessage();
        }
    }
}