— Scott McNealy, Sun Microsystems Chairman, President and ceo

a constructor if the compiler 
writes one for you?
A: 
If you need code to help 
initialize your object and get 
it ready for use, you’ll have to 
write your own constructor. You 
might, for example, be depen-
dent on input from the user 
before you can finish making 
the object ready. There’s another 
reason you might have to write 
a constructor, even if you don’t 
need any constructor code 
yourself. It has to do with your 
superclass constructor, and we’ll 
talk about that in a few minutes.
Q:
How can you tell a con-
structor from a method? Can 
you also have a method that’s 
the same name as the class?
A: 
Java lets you declare a 
method with the same name as 
your class. That doesn’t make it 
a constructor, though. The thing 
that separates a method from a 
constructor is the return type. 
Methods must have a return 
type, but constructors cannot 
have a return type.
Q:
Are constructors inher-
ited? If you don’t provide a 
constructor but your superclass 
does, do you get the superclass 
constructor instead of the 
default?
A: 
Nope. Constructors are 
not inherited. We’ll look at that in 
just a few pages.
*Instance variables do have a default value. 0 or 
0.0 for numeric primitives, false for booleans, and 
null for references.

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244
 
chapter 9
Using the constructor to initialize 
important Duck state*
If an object shouldn’t be used until one or 
more parts of its state (instance variables) have 
been initialized, don’t let anyone get ahold of 
a Duck object until you’re fi nished initializing! 
It’s usually way too risky to let someone make—
and get a reference to—a new Duck object that 
isn’t quite ready for use until that someone turns 
around and calls the setSize() method. How will 
the Duck-user even know that he’s required to call 
the setter method after making the new Duck?
The best place to put initialization code is in the 
constructor. And all you need to do is make a 
constructor with arguments.