— Scott McNealy, Sun Microsystems Chairman, President and ceo

overloaded and default 
constructors
Doesn’t the compiler always 
make a no-arg constructor 
for you?
OK, let’s see here... “You 
have the right to your own 
constructor.” Makes sense.
“If you cannot afford a constructor, 
one will be provided for you by the 
compiler.” Good to know.
No!

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constructors and 
gc
you are here
4
247
 BULLET POINTS
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Instance variables live within the object they belong to, on 
the Heap.
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If the instance variable is a reference to an object, both 
the reference and the object it refers to are on the Heap.
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A constructor is the code that runs when you say 
new
on 
a class type.
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A constructor must have the same name as the class, and 
must not have a return type.
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You can use a constructor to initialize the state (i.e. the 
instance variables) of the object being constructed.
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If you don’t put a constructor in your class, the compiler 
will put in a default constructor.
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The default constructor is always a no-arg constructor.
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If you put a constructor—any constructor—in your class, 
the compiler will not build the default constructor.
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If you want a no-arg constructor, and you’ve already put 
in a constructor with arguments, you’ll have to build the 
no-arg constructor yourself.
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Always provide a no-arg constructor if you can, to make it 
easy for programmers to make a working object. Supply 
default values.
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Overloaded constructors means you have more than one 
constructor in your class.
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Overloaded constructors must have different argument 
lists.
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You cannot have two constructors with the same 
argument lists. An argument list includes the order and/or 
type of arguments.
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Instance variables are assigned a default value, even 
when you don’t explicitly assign one. The default values 
are 0/0.0/false for primitives, and null for references.
Four different constructors 
means four different ways to 
make a new mushroom.