User Interface
In android user interface is mainly built using View and ViewGroup objects.View objects are the basic units of user interface and also View object is a data structure whose properties store the layout parameters and content for a specific rectangular area of the screen.
View Hierarchy
On the Android platform, you define an Activity's UI using a hierarchy of View and ViewGroup nodes,
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Layout
The most common way to define your layout and express the view hierarchy is with an XML layout file.
Widgets
Widget is a user interface which input the user value.mainly used widgets are button,check box,Text field are the mainly used widgets.
Menus
Menu is one of the another UI.which also input the value from the user.Context menu.Optional menu are the mainly used UI menus used in android.
