Java Reference
In-Depth Information
a compilation error will occur. Thus,
public
classes
Account
and
AccountTest
(Fig. 3.2)
must
be declared in the
separate
files
Account.java
and
AccountTest.java
, respectively.
Every class declaration contains the keyword
class
followed immediately by the
class's name—in this case,
Account
. Every class's body is enclosed in a pair of left and right
braces as in lines 6 and 20 of Fig. 3.1.
Identifiers and Camel Case Naming
Class names, method names and variable names are all
identifiers
and by convention all use
the same
camel case
naming scheme we discussed in Chapter 2. Also by convention, class
names begin with an initial
uppercase
letter, and method names and variable names begin
with an initial
lowercase
letter.
Instance Variable
name
Recall from Section 1.5 that an object has attributes, implemented as instance variables
and carried with it throughout its lifetime. Instance variables exist before methods are
called on an object, while the methods are executing and after the methods complete exe-
cution. Each object (instance) of the class has its
own
copy of the class's instance variables.
A class normally contains one or more methods that manipulate the instance variables be-
longing to particular objects of the class.
Instance variables are declared
inside
a class declaration but
outside
the bodies of the
class's methods. Line 7
private
String name;
// instance variable
declares instance variable
name
of type
String
outside
the bodies of methods
setName
(lines
10-13) and
getName
(lines 16-19).
String
variables can hold character string values such
as
"Jane
Green"
. If there are many
Account
objects, each has its own
name
. Because
name
is an instance variable, it can be manipulated by each of the class's methods.
Good Programming Practice 3.1
We prefer to list a class's instance variables first in the class's body, so that you see the names
and types of the variables before they're used in the class's methods. You can list the class's
instance variables anywhere in the class outside its method declarations, but scattering the
instance variables can lead to hard-to-read code.
Access Modifiers
public
and
private
Most instance-variable declarations are preceded with the keyword
private
(as in line 7).
Like
public
,
private
is an
access modifier
. Variables or methods declared with access mod-
ifier
private
are accessible only
to methods of the class in which they're declared
.
So, the
variable
name
can be used only in each
Account
object's methods (
setName
and
getName
in
this case). You'll soon see that this presents powerful software engineering opportunities.
setName
Method of Class
Account
Let's walk through the code of
setName
's method declaration (lines 10-13):
public void
setName(String name)
{
this
.name = name;
// store the name
}
This line is the method header
