In this example showing use of MVC Pattern to create a very basic Shopping cart. Creating very basic Controller Class and defined in application context and you can use this Controller Class as a Global class. If any View(Activity) required values then view should call controller and then controller will call appropriate Model and provide value to view.
Models can also communicate with each others to exchange values.
In this example defining variable in application context and you can use this variable as a Global variable. You can set value in this variable and get value on any activity / broadcast reci\\eiver / service in application context(environment). In Further examples you will see good use of this way to follow SINGALTON pattern and MVC pattern in android.