— Scott McNealy, Sun Microsystems Chairman, President and ceo

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chapter 10
Getting an object that extends Calendar
How in the world do you get an “instance” of an abstract class? 
Well you don’t of course, this won’t work:
This WON’T work:
Calendar cal = new Calendar();
Instead, use the static “getInstance()” method:
Calendar cal = Calendar.getInstance();
Wait a minute. 
If you can’t make an 
instance of the Calendar 
class, what exactly are you 
assigning to that Calendar 
reference?
You can’t get an instance of Calendar, 
but you can can get an instance of a 
concrete Calendar subclass.
Obviously you can’t get an instance of Calendar, because 
Calendar is abstract. But you’re still free to call static methods 
on Calendar, since static methods are called on the class, 
rather than on a particular instance. So you call the static 
getInstance() on Calendar and it gives you back... an instance 
of a concrete subclass. Something that extends Calendar 
(which means it can be polymorphically assigned to Calendar) 
and which—by contract—can respond to the methods of class 
Calendar.
In most of the world, and by default for most versions of Java, 
you’ll be getting back a java.util.GregorianCalendar instance.
The compiler won’t allow this!
This syntax should look familiar at this 
point - we’re invoking a static method.
getting a 
Calendar

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numbers 
and
statics
you are here
4
305
Working with Calendar objects
There are several key concepts you’ll need to understand in 
order to work with Calendar objects:
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Fields hold state - A Calendar object has many fields that are used to 
represent aspects of its ultimate state, its date and time. For instance, you 
can get and set a Calendar’s year or month.
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