Java Reference
In-Depth Information
class FictionalCharacter
name: String
setName(String)
getName():String
class Villain
class Superhero
evilPower:int
narcissim: int
goodPower:int
respect: int
FIGURE 8.2:
Class inheritance example.
The inheritance relationship is also referred to as an
is-a
relationship. For example,
a superhero
is-a
fictional character. The subclass inherits all the attributes and method
of the superclass.
In Java, the
extends
keywords is used to denote inheritance. Note that both
Superhero
and
Villain
extend from
FictionalCharacter
.The
FictionalCharacter
class is the
superclass
, while the
Superhero
and
Villain
classes are the
subclasses
.
The new design helped us avoid defining the variable
name
and the
setName
and
getName
methods multiple times. Note that inside the
Superhero
class we do not have direct access to
the name of the superhero. The reason is that the variable
name
is
private
and therefore it is
only accessible from within the
FictionalCharacter
class. However, inside the
Superhero
class we have access to the
FictionalCharacter
by using the
super
keyword. The
super
keyword is similar to the
this
keyword. However, instead of giving us access to the current
object, it gives us access to the super object (i.e., the object of the superclass). For example,
if we put the following code inside a method of the
Superhero
class, it will print the name
of the superhero.
System. out . println (
super
.getName());
Class inheritance is similar to class containment. If the
Superhero
class inherits from
the
FictionalCharacter
class, then every object of type
Superhero
will have an object
of type
FictionalCharacter
inside it. Figure 8.3 shows an example object for Superman.
As a superhero, he has values for
goodPower
and
respect
. In other words, we could have
defined the
Superhero
classasfollows.
public class
Superhero
{
private int
goodPower ;
private int
respect ;
...
private
FictionalCharacter superObject ;
}
Since a
Superhero
is a type of
FictionalCharacter
and a
Superhero
does not have a
FictionalCharacter
inside it, the first design is obviously better. After all, we want our
design to follow the scenario that we are modeling as closely as possible.
