The next step is to implement the ApplicationLayout interface and add the required methods:

• void addHeaderComponent(Component)
• void addWorkingAreaComponent(WorkingAreaComponent)
• Collection<Component> getHeaderComponents()
• Collection<WorkingAreaComponent> getWorkingAreaComponents()
• void addMenuOption(MenuOption, SerializableConsumer<MenuOption>)

Implementing the addHeaderComponent(Component) method is quite straightforward:

@Override
public void addHeaderComponent(Component component) {
    component.setWidth(null);
    header.addComponent(component);
    header.setComponentAlignment(component,
            Alignment.MIDDLE_RIGHT);
}

The addWorkingAreaComponent(WorkingAreaComponent) method should avoid adding two tabs with the same caption. Instead of adding the same tab twice it should select the corresponding existing tab. A Collection is used to keep track of the added components, as shown in the following code:

public class TabBasedApplicationLayout extends CustomComponent
        implements ApplicationLayout {
    ...

    private Collection<WorkingAreaComponent> workingAreaComponents
            = new HashSet<>();

    @Override
    public void addWorkingAreaComponent(WorkingAreaComponent
            component) {
        addWorkingAreaComponent(component, true);
    }

    public void addWorkingAreaComponent(WorkingAreaComponent
            component, boolean closable) {
        if (!workingAreaComponents.contains(component)) {
            TabSheet.Tab tab = tabSheet.addTab(
                    component.getComponent(),
                            component.getCaption());
            tab.setClosable(closable);
            tabSheet.setSelectedTab(tab);
            workingAreaComponents.add(component);
        } else {
            showComponent(component.getCaption());
        }
    }

    public void showComponent(String caption) {
        IntStream.range(0, tabSheet.getComponentCount())
                .mapToObj(tabSheet::getTab)
                .filter(tab -> tab.getCaption().equals(caption))
                .forEach(tabSheet::setSelectedTab);
    }
}

Because this concrete implementation is based on a TabSheet where each tab can or cannot be closed, it makes sense to overload the ApplicationLayout.addWorkingAreaComponent(WorkingAreaComponent) method to allow clients to specify this behavior.

An interesting part of the previous code is the showComponent(String) method, which selects a tab by its caption. This method uses an IntStream to loop through the tabs in the TabSheet. This method is equivalent to the following one:

public void showComponent(String caption) {
   for(int i = 0; i < tabSheet.getComponentCount(); i++) {
       TabSheet.Tab tab = tabSheet.getTab(i);
 
       if(tab.getCaption().equals(caption)) {
           tabSheet.setSelectedTab(tab);
       }
   }
}

The next method to implement is getHeaderComponents():

@Override
public Collection<Component> getHeaderComponents() {
    return IntStream.range(0, header.getComponentCount())
            .mapToObj(header::getComponent)
            .collect(Collectors.toList());
}

This method uses an IntStream similar to the one in the showComponent(String) method. A Collector is used to create a List containing all the components in the header.

Since we already have a Collection object with all the components in the working area, the getWorkingAreaComponents() method implementation is just a regular getter:

@Override
public Collection<WorkingAreaComponent> getWorkingAreaComponents() {
    return workingAreaComponents;
}