Android Fundamental UI DesignUser Interface design, human–computer interaction important that you get them right when creating your User Interfaces. Android introduces some new terminology for familiar programming metaphors that will be explored in detail in the following sections:
Views are the basic User Interface class for visual interface elements commonly known as controls or widgets. All User Interface controls, and the layout classes, are derived from Views
View Groups are extensions of the View class that can contain multiple child Views. By extending the ViewGroup class, you can create compound controls that are made up of interconnected child Views. The ViewGroup class is also extended to provide the layout managers, such as LinearLayout, that help you compose User Interfaces
Activities represent the window or screen being displayed to the user. Activities are the Android equivalent of a Form. To display a User Interface, you assign a View or layout to an Activity. Android provides several common UI controls, widgets, and layout managers.