code: private void initLayout() {
  
          VerticalLayout page = new VerticalLayout();
          setContent(page);
          page.setId("page");
  
          page.addComponent(headerLayout);
          initLayoutHeader();
  
          page.addComponent(mainTab);
  
  
          initLayoutFooter();
          page.addComponent(layoutFooter);
  
      }
docs: /*
  In this example layouts are programmed in Java. You may choose use a
  visual editor, CSS or HTML templates for layout instead.