public class Tasks{
private int id;
private Double duration;

public StakeholderTasks(int i, String string) {
    this.id = id;
    this.taskName=taskName;
    // TODO Auto-generated constructor stub
}
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public Double getDuration() {
    return duration;
}

public void setDuration(Double duration) {
    this.duration = duration;
}
}

public class stakeholderImpl extends CustomComponent {
private Grid<Tasks> grid1;
private Binder<Tasks> binder = new Binder<>(Tasks.class);
cmpy =  datastoreinstance.updateTaskList();
provider1 = new ListDataProvider<>(cmpy );
grid1 = new Grid<>();
grid1.addColumn(Tasks::getDuration);
grid1.asSingleSelect().addValueChangeListener(event -> {

            form.setVisible(false);

                window = createWindow(window,
                        ((MainUI) (UI.getCurrent())).getLanguageMessage("general.addnewtask"),
                        event.getValue(), "EDIT",form);
            } catch (ClassNotFoundException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            } catch (SQLException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
}

        }

    });
binder.forField(duration).asRequired(((MainUI)       (UI.getCurrent())).getLanguageMessage("general.required"))
        .withValidator(new RegexpValidator(((MainUI) (UI.getCurrent())).getLanguageMessage("general.numerror"), DBConstants.regex))
        .bind(taskdetails -> nf_out.format(stakeholders.getDuration()),
                        (taskdetails, formValue) -> {
                            NumberFormat nf_in = NumberFormat.getNumberInstance(Locale.GERMANY);
                            double val = 0d;
                            try {
                                    val = nf_in.parse(formValue).doubleValue();
                                    taskdetails.setDuration(val);
                            } catch (ParseException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }
                            });
}