Constructors and Inheritance (extends)
======================================


1) a constructor may explicitly invoke the constructor of a super-class
by using the special "super" syntax. 

2) this statement must be the very *first* statement in the body of the
constructor. 

3) we may choose to pass on arguments as we like.

e.g. (also see source code supplied)

 public B() {

   super();
   ...
 }

or

 public B() {

   super(17);
   ...
 }

4) if we do not use any "super(...)" statement explicitly, the compiler 
will insert the call "super()" as the first statement of the
constructor for us.

Therefore the following two are equivalent:

 public B() { super(); }

and 

 public B() { }

5) a subclass can only call constructors that are actually present
in the superclass. Therefore the following DOES NOT work:

 public B() { super(1,2,3); }

6) data fields (also called data members) are initialised BEFORE the
constructor is run (again see java code).

7) data fields that are not explicitly initialised will still have
a "reasonable" value: e.g. 0 for ints, false for booleans, null for 
data-fields that hold references to objects (i.e. instances of some
class) and so on (again see java code).