The following is an overview of the main java packages in API in android SDK:

android.app  : provides the high-level program model, provides the basic running environment
android.content  : contains various classes that access and publish data on the device
android.database  : browses and operates the database through the content provider
android.graphics  : the underlying graphics library, including the canvas, color filter, dot, and rectangle, can be drawn directly to the screen .
android.location  : classes that locate and relate services
android.media  : provide 1 These classes manage a variety of audio and video media interfaces
android.net  : provides help with network access to more than usual classes java.net.*  interface
android.os  : provides system services, message transmission, IPC  mechanism
android.opengl  : provide OpenGL The tools
android.provider  : provides class access Android Content provider of
android.telephony  : provide information related to making phone calls API interaction
android.view  : provides the basic user interface framework
android.util  : involves instrumental methods, such as time and date manipulation
android.webkit  : default browser interface
android.widget  : contains a variety of UI Elements (most of which are visible) are used on the application's screen