Inheritance

[Kamila Jolan]

Hello,

Can somebody help me understand why this code:

  
class Parent {  

String s= "Parent";
void someMethod() {   System.out.println(s);  } 

void show() {  
   someMethod();
   System.out.println(s);  
     }  

 }  
   
 class Child extends Parent {  

String s= "Child";
void someMethod() {   System.out.println(s);  } 

 }  
  
 public class Test {  
     public static void main(String[] args) {  
         Parent parent = new Child();
       parent. show() ; //or  new Child ().show ();
        
     }  
 }  


  

giving the following results :
Child
Parent
I understand why the "Child" is appearing - the overridden method "someMethod()" will be invoked and it will use the "s" variable from the Child class. That is why I don't know why the show() method will use the "s" variable from the Parent class in the second case (line 9). The Child object is created and the show() method is inherited by the Child class.

Any help will be appreciated

[Henry Wong]

Kamila Jolan wrote:That is why I don't know why the show() method will use the "s" variable from the Parent class in the second case (line 9). The Child object is created and the show() method is inherited by the Child class.

Inheriting doesn't mean that the compiler will get the source for the parent method and recompile it for the child. If the child doesn't override the method, the parent's version of the method is called -- and the parent's version of the show() method only knows about the parent reference the string. Polymorphism doesn't apply to instance variables.

Henry

[himanshu.harish agrawal]

Henry Wong wrote:

Kamila Jolan wrote:That is why I don't know why the show() method will use the "s" variable from the Parent class in the second case (line 9). The Child object is created and the show() method is inherited by the Child class.

Polymorphism doesn't apply to instance variables.

Henry

The statement quoted by Henry is the main concept. As Polymorphism applies only for the methods (only instance not even static methods), JVM took the polymorphic method show() but for the field it took original field of the class.

Thanks.

[Kamila Jolan]

Thanks a lot