Inheritance in java: relationships between parent and child classes

When a parent class reference is directed to a child class object

1, the Kawai class overrides a method, the parent class references a new method that calls the subclass to redefine

2. The Kawai class does not overwrite a method, the parent class references the old method that calls the parent class itself

3. The Kawai class overrides a property, but the parent class reference still calls the old property of the parent class itself

4. The Kawai class does not overwrite a property, the parent class refers to the old property that invokes the parent class itself

5. The parent class reference cannot access the new defined method of the child class

When a subclass reference points to its own object

1. Kawai class overrides a method, the subclass references a new method that calls the subclass to redefine

2. The Kawai class does not overwrite a method, the child class references the old method that calls the parent class itself

3. Kawai class overrides a property, the subclass references the new attribute redefined by the calling subclass

4, the Kawai class does not overwrite a property, the subclass reference invokes the old property of the parent class itself

5. The subclass reference can access the new defined method of the child class

C. Sample code B.java [java]View PlainCopy 

2. Public class B {
6. int a = 1;
8. int b = 2;
12. void F1 () {
14. System.out.println ("b.f1 ()");
16. }
20. void F2 () {
22. System.out.println ("b.f2 ()");
24. }
28. }

C.java [java]View PlainCopy  

2. Public class C extends B {
6. int a = 3;
10. @Override
12. void F1 () {
14. System.out.println ("c.f1 ()");
16. }
20. void F3 () {
22. System.out.println ("c.f3 ()");
24. }
28. public static void main (string[] Args) {
32. b b = new C (); Parent class reference to child class object
34. B.F1 (); The//subclass overrides the method, so the parent class reference calls the new method
36. B.f2 (); The//subclass does not overwrite the method, so the parent class reference calls the old method
38. ///b.f3 (); This line removes the comment error, the parent class reference cannot access the child class new definition method
40. System.out.println (b.a); The//subclass overrides the property, but the parent class reference still accesses the old property
42. System.out.println (b.b); //subclass does not overwrite this property, parent class accesses old property
46. System.out.println ();
50. c C = new C (); The subclass reference points to its own object
52. C.F1 (); The//subclass overrides the parent class method, so the new method is called
54. C.f2 (); The//subclass does not overwrite the parent class method, so the old method is called
56. C.F3 (); //subclass calls its own new defined method
58. System.out.println (c.a); //subclass overrides this property, so access the new property
60. System.out.println (c.b); //subclass does not overwrite this property, so access the old property
62. }
64. }

Output: [html]View PlainCopy 

1. C.F1 ()
2. B.f2 ()
3. 1
4. 2
6. C.F1 ()
7. B.f2 ()
8. C.F3 ()
9. 3
10. 2

Inheritance in java: relationships between parent and child classes