Java Reference
In-Depth Information
C
n
C
n-1
C
2
C
1
. . . . .
If
o
is an instance of
C
1
,
o
is also an
instance of
C
2
,
C
3
, …,
C
n-1
, and
C
n
java.lang.Object
F
IGURE
11.2
The method to be invoked is dynamically bound at runtime.
Listing 11.6 gives an example to demonstrate dynamic binding.
L
ISTING
11.6
DynamicBindingDemo.java
1
public class
DynamicBindingDemo {
2
VideoNote
Polymorphism and dynamic
binding demo
public static void
main(String[] args) {
m(
new
GraduateStudent());
3
4 m(
new
Student());
5 m(
new
Person());
6 m(
new
Object());
7 }
8
9
public static void
{
10 System.out.println(x.toString());
11 }
12 }
13
14
class
polymorphic call
m(Object x)
dynamic binding
GraduateStudent
extends
Student
{
15 }
16
17
class
Student
extends
Person
{
18 @Override
19
override
toString()
toString()
public
String
{
20
return
"Student"
;
21 }
22 }
23
24
class
Person
extends
Object
{
25 @Override
26
override
toString()
public
String
toString()
{
27
return
"Person"
;
28 }
29 }
Student
Student
Person
java.lang.Object@130c19b
Method
m
(line 9) takes a parameter of the
Object
type. You can invoke
m
with any object
(e.g.,
new GraduateStudent()
,
new Student()
,
new Person()
, and
new Object()
)
in lines 3-6).
When the method
m(Object x)
is executed, the argument
x
's
toString
method is
invoked.
x
may be an instance of
GraduateStudent
,
Student
,
Person
, or
Object
. The
classes
GraduateStudent
,
Student
,
Person
, and
Object
have their own implementa-
tions of the
toString
method. Which implementation is used will be determined by
x
's
actual type at runtime. Invoking
m(new GraduateStudent())
(line 3) causes the
toString
method defined in the
Student
class to be invoked.
Invoking
m(new Student())
(line 4) causes the
toString
method defined in the
Student
class to be invoked; invoking
m(new Person())
(line 5) causes the
toString
