Card      c;
Valentine v;
Birthday  b;
Holiday   h

c = new Valentine("Debby", 8);    //OK
b = new Valentine("Elroy", 3);    //WRONG
v = new Valentine("Fiona", 3);    //OK
h = new Birthday ("Greg",  35);   //WRONG

Another Hierarchy

Here is a picture of another hierarchy: There are no abstract classes in this hierarchy, so each class can be instantiated. As seen previously, the following is OK:

parentReference = childReference

A parent reference variable can hold a reference to an object of one of its child types (or a reference to one of their child types, and so on.) However, the opposite direction

// don't do this
childReference = parentReference

can not be done, unless the parentReference actually refers to a child object (this is rare.)

Here are some variables:

Rodent     rod;
Rat        rat;
Mouse      mou;

Look at the table and decide if each section of code is correct or not.

code section	OK or Not?	code section	OK or Not?
rod = new Rat();		rod = new FieldMouse();
mou = new Rat();		mou = new Rodent();
rat = new Rodent();		rat = new LabRat();
rat = new FieldMouse();		rat = new Mouse();