android views, widgets, view groups, layouts, containers

The user interface is implemented as collection of view objects (e.g., a date widget, or editable text) -- a view is a class and a widget (e.g., a button) which is drawn on some part of the screen and is responsible for event handling such as when the user interacts with the UI (e.e., clicks on a button, enters the date). User's can construct sophisticated UIs by bundling views together using layouts (or ViewGroups) which can be considered as invisible containers. These containers can hold child containers. Each container defines its views (or other ViewGroups) and their layout properties.