gistfile1.java

public class Voyage {
  private Country targetcountry;
  private int capacity;
  private List<Cargo> items = Constraints.constrainedList(new ArrayList<Cargo>(), new Constraint<Cargo>() {
    @Override
    public Cargo checkElement(Cargo cargo) {
      Preconditions.checkNotNull(cargo);
      Preconditions.checkArgument(targetcountry.allows(cargo));
      Preconditions.checkArgument(cargo.getUnits() > 0);
      return cargo;
    }
  });

  public void load(List<Cargo> cargos) {
    items.addAll(cargos);
  }
}