Implementing a CRUD using Grids and forms

In this section, we'll develop a CRUD user interface using modal pop-up windows to show a form for adding and editing User instances. The following is a screenshot of the finished form:

Let's start with the following component:

public class CustomCrud extends Composite {

private Button refresh = new Button("", VaadinIcons.REFRESH);
    private Button add = new Button("", VaadinIcons.PLUS);
    private Button edit = new Button("", VaadinIcons.PENCIL);

    private Grid<User> grid = new Grid<>(User.class);

    public CustomCrud() {
        initLayout();
initBehavior();
refresh();
}

private void initLayout() {
CssLayout header = new CssLayout(refresh, add, edit);
header.addStyleName(ValoTheme.LAYOUT_COMPONENT_GROUP);

grid.setSizeFull();

VerticalLayout layout = new VerticalLayout(header, grid);
layout.setExpandRatio(grid, 1);
setCompositionRoot(layout);
setSizeFull();
}

private void initBehavior() {
    }

    public void refresh() {...