Java Reference
In-Depth Information
4.2
Anatomy of a Class
SR 4.5
A class is the blueprint of an object. It defines the variables and methods
that will be a part of every object that is instantiated from it. But a class
reserves no memory space for variables. Each object has its own data
space and, therefore, its own state.
SR 4.6
The instance data of the
Die
class are
MAX
, an integer constant equal to
6 that represents the number of faces on the die and therefore the maxi-
mum value of the die, and
faceValue
, an integer variable that represents
the current “up” or face value of the die.
SR 4.7
The methods defined for the
Die
class that can change the state of a
Die
object are
roll
and
setFaceValue
.
SR 4.8
When you pass an object to a
print
or
println
method, the
toString
method of the object is called automatically to obtain a string descrip-
tion of the object. If no
toString
method is defined for the object, then
a default string is used. Therefore, it is usually a good idea to define a
toString
method when defining classes.
SR 4.9
The scope of a variable is the area within a program in which the vari-
able can be referenced. An instance variable, declared at the class level,
can be referenced in any method of the class. Local variables, including
the formal parameters, declared within a particular method, can be ref-
erenced only in that method.
SR 4.10
A UML diagram helps us visualize the entities (classes and objects)
in a program as well as the relationships among them. UML dia-
grams are tools that help us capture the design of a program prior
to writing it.
4.3
Encapsulation
SR 4.11
A self-governing object is one that controls the values of its own data.
Encapsulated objects, which don't allow an external client to reach in
and change its data, are self-governing.
SR 4.12
An object's interface is the set of public operations (methods) defined
on it. That is, the interface establishes the set of services the object will
perform for the rest of the system.
SR 4.13
A modifier is a Java reserved word that can be used in the definition of
a variable or method and that specifically defines certain characteristics
of its use. For example, by declaring a variable with private visibility,
the variable cannot be directly accessed outside of the object in which it
is defined.
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