Most of the applications you create in Android will fall into one of the following categories:
- Foreground — An application that’s useful only when it’s in the foreground and is effectively suspended when it’s not visible. Games are the most common examples
- Background — An application with limited interaction that, apart from when being confi-gured, spends most of its lifetime hidden. These applications are less common, but good examples include call screening applications, SMS auto-responders, and alarm clocks
- Intermittent — Most well-designed applications fall into this category. At one extreme are applications that expect limited interactivity but do most of their work in the background. A common example would be a media player. At the other extreme are applications that are typically used as foreground applications but that do important work in the background. Email and news applications are great examples.
- Widgets and Live Wallpapers — Some applications are represented only as a home-screen Widget or as a Live Wallpaper.