— Scott McNealy, Sun Microsystems Chairman, President and ceo

particularly motivating.

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184
 
chapter 7
the way 
polymorphism 
works
Dog myDog 
= new Dog();
Tells the JVM to allocate space for a 
reference variable. The reference variable 
is, forever, of type Dog. In other words, 
a remote control that has buttons to 
control a Dog, but not a Cat or a Button 
or a Socket. 
1
Declare a reference 
variable
Dog
myDog
Dog myDog =
 new Dog();
Tells the JVM to allocate space for 
a new Dog object on the garbage 
collectible heap.
2
Create an object
Dog myDog = new Dog();
The 3 steps of object 
declaration and assignment
1
2
3
Dog object
Dog myDog
 
=
 
new Dog();
Assigns the new Dog to the refer-
ence variable myDog. In other words, 
program the remote control.
3
Link the object 
and the reference
Dog object
Dog
myDog
To see how polymorphism 
works, we have to step back 
and look at the way we 
normally declare a reference 
and create an object...

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inheritance and 
polymorphism
you are here
4
185
The important point is that the 
reference type AND the object 
type are the same. 
In this example, both are Dog.
Dog
myDog
Dog object 
These two are the same type. The reference 
variable type is declared as Dog, and the object 
is created as new Dog().
But with polymorphism, the 
reference and the object can 
be 
different.