Resources are separate from the source code. In Android,
all non code resources are defined in XML files. For every
resource that included in an Android project, the SDK build
tools define a unique integer ID, which can be used to
reference the resource from the application code or from
other resources defined in XML files. Providing resources
separate from source code makes it easy to update various
characteristics of an application without modifying code and
by providing sets of alternative resources enables developers
to optimize the application for a variety of device
configurations, such as different languages and screen sizes