The difference between polymorphism and C + + polymorphism in Java

Source: http://blog.csdn.net/hihui/article/details/8604779

2. #include <stdio.h>
6. Class Base
8. {
10. Public
12. int i;
16. Base ()
18. {
20. i = 99;
22. Amethod ();
24. }
28. virtual void Amethod ()
30. {
32. printf ("Base.amethod () \ n");
34. }
38. };
42. Class Derived: Public Base
44. {
46. Public
48. int i;
52. Derived () {
54. i =-1;
56. }
60. virtual void Amethod ()
62. {
64. printf ("Derived.amethod () \ n");
66. }
70. };
74. int main (int argc, char *argv[])
76. {
78. Base *b = new Derived ();
80. printf ("%d\n", b->i);
82. B->amethod ();
84. }

The output is:

Base.amethod ()
99
Derived.amethod ()

The same Java code

[Java]View Plaincopy

2. Class Base
4. {
6. int i = 99;
10. public void Amethod ()
12. {
14. System.out.println ("Base.amethod ()");
16. }
20. Base ()
22. {
24. Amethod ();
26. }
28. }
32. Class Derived extends Base
34. {
36. int i =-1;
40. public void Amethod ()
42. {
44. System.out.println ("Derived.amethod ()");
46. }
50. public static void Main (String argv[])
52. {
54. Base B = new Derived ();
56. System.out.println (B.I);
58. B.amethod ();
60. }
62. }

It outputs the result of

Derived.amethod ()
99
Derived.amethod ()

The difference is reflected in the first line of output;

This line is output in the derived constructor, derived itself does not have a constructor, it only calls the parent class's constructor, that is, Base's Amethod ();

For C + + code, the execution is Base::amethod ();

For Java code, the execution is Derived::amthod ();

Why, when calling the base class's Amethod in C + +, the subclass is not ready yet, so the amethod of the base class is executed.

The difference between polymorphism and C + + polymorphism in Java