Prentice.Hall.Introduction.to.Java.Programming,.Brief.Version.9th.(2014).[sharethefiles.com]

11.8 Dynamic Binding 423
C n C n-1 . . . . .
C 2 C 1
java.lang.Object
If o is an instance of C 1 , o is also an
instance of C 2 , C 3 , …, C n-1 , and C n
FIGURE 11.2
The method to be invoked is dynamically bound at runtime.
Listing 11.6 gives an example to demonstrate dynamic binding.
LISTING 11.6
DynamicBindingDemo.java
1 public class DynamicBindingDemo {
2 public static void main(String[] args) {
3
4
m(new GraduateStudent());
m(new Student());
5 m(new Person());
6 m(new Object());
7 }
8
9 public static void m(Object x) {
10 System.out.println(x.toString());
11 }
12 }
13
14 class GraduateStudent extends Student {
15 }
16
17 class Student extends Person {
18 @Override
19 public String toString() {
20 return "Student";
21 }
22 }
23
24 class Person extends Object {
25 @Override
26 public String toString() {
27 return "Person";
28 }
29 }
VideoNote
Polymorphism and dynamic
binding demo
polymorphic call
dynamic binding
override toString()
override toString()
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 implementations
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