Using composition to develop custom components
If extending VerticalLayout is a problem, a possible solution is to not extend any class at all. However, in that case, we wouldn't get a Component, but a class of which instances cannot be added to the components tree. What about extending a more suitable component in the hierarchy? Let's start with interfaces. The following figure shows some of the top interfaces in the hierarchy:
Going up the hierarchy, we find the Component interface which has more than 20 methods that would require an implementation. The other interfaces inherit these 20+ methods and add some more. Fortunately, Vaadin provides abstract implementations for these interfaces. The following figure shows some of the equivalent implementations:
AbstractComponent is the default implementation of Component. Many Vaadin components directly extend this class. It's not a convenient class for the login form, though, since it's too general and doesn't offer methods to add other components...
