Calendar cal = Calendar.getInstance(); returns GregorianCalendar, how can methods be executed in that case?

Question

Java

Calendar cal = Calendar.getInstance(); returns a GregorianCalendar, how then can the methods of GregorianCalendar be executed if java is looking at the methods of the reference variable and not at the referenced object?
And why use the construction Calendar cal = Calendar.getInstance(); instead of GregorianCalendar var = new GregorianCalendar() ?

Answer 1

Calendar is an abstract class. GregorianCalendar extends it.
You need to work with Calendar and not think about a specific implementation.
Depending on the locale, a type other than GregorianCalendar may be returned.