ObservableList<Person> items = FXCollections.observableArrayList();
items.add(new Person("Hans","Meier",22));
items.add(new Person("Eva","Becker",23));
items.add(new Person("Max","Schmitt",24));

list.getSelectionModel().selectedItemProperty().addListener(
    new ChangeListener<Person>() {
      public void changed(ObservableValue<? extends Person> ov,
        Person old_val, Person new_val) {
          System.out.println(new_val.getAlter());
      }
    });