Java Fundamentals Hardening 11: Two basic problems of polymorphism

1. Question 1th

1 classBase {2      Public voidmethod () {3System.out.print ("Base method"));4     }5 }6 7 classChildextendsBase {8      Public voidMethodB () {9System.out.print ("Child MethodB");Ten     } One } A  - classSample { -      Public Static voidMain (string[] args) { theBase base =NewChild (); - Base.methodb (); -     } -}

A. Base method

B. Child MethodB

C. Base method Child MethodB

D. Compilation errors

2. Question 2nd

1 classPerson {2     intA;3      Public intChangeintm) {4         returnm;5     }6 }7 8  Public classTeacherextendsPerson {9      Public intb;Ten      Public Static voidMain (string[] args) { OnePerson p =NewPerson (); ATeacher T =NewTeacher (); -         inti; -______//fill in the code here the     } -}

A.i=b;

B.i=a;

C.i=p.change (30);

d.i=t.b;

3.

Attention:

(1) For member variables: compile look left , run look left ;

(2) For member method: compile look left , run look right ;

(3) Question 1th: The parent class refers to a subclass that can only invoke a method inherited from a parent class or a subclass to override a method inherited from a parent class;

Question 2nd: Static methods cannot invoke non-static members, static members belong to classes, main belongs to subclasses, it is also methods, but static methods of static, only static variables can be called. Therefore,int A and int b

are not directly called directly in main .

Java Fundamentals Hardening 11: Two basic problems of polymorphism