Explain on Casting

Question

2 derived class:
Class Animal is the base class. Class Dog is the derived class of Animal. Class Spaniel is the derived class of Class Dog.
Spaniel aPet = new Spaniel("Fang"); //statement 1
Animal theAnimal = (Animal)aPet; //statement 2
Animal theAnimal = aPet; //statement 3
Dog aDog = (Dog)theAnimal; //statement 4
What is the difference between statements 2 and 3?
From the point of memory referencing, what is statement 2 doing?
I know that creating a object variable is assigning a memory location to point to an area of memory that contains the object information. But casting a derived class or a superclass to a class, what is actually happening?

Answer 1

Here is my understanding of casting. There is no difference between statements 2 and 3. Java does not require an explicit cast when upcasting. There is no affect on memory when you do upcasting. Basically, a Spaniel needs to be in memory because you may downcast back to a Spaniel. I wrote the following code to test these statement. Note: timestamp inherits from Date.
java.sql.Timestamp ts = java.sql.Timestamp.valueOf("2002-1-15 3:45:11.5555");
java.util.Date dt = ts;
// java.util.Date dt = (java.util.Date)ts;
if (dt instanceof java.sql.Timestamp) System.out.println("Is a timestamp");
else System.out.println("Not a timestamp");
Running this will indicate that dt is a timestamp regardless of how you assign dt.