method overriding and visibility promotion.

[Rashid Mian]

   package chapters.p1;
 
public class SuperClass {
 
public SuperClass() {
super();
// TODO Auto-generated constructor stub
}
protected void smile(int i){System.out.println("Super Mama Super");}

 
}
 
-----------
package chapters.p2;
import chapters.p1.SuperClass;
public class SubClass  extends SuperClass{
 
public SubClass() {
super();
// TODO Auto-generated constructor stub
}
 public void smile(int i){System.out.println("Sub Mama Sub");}

}
-----------------
package chapters.p3;
import chapters.p1.SuperClass;
import chapters.p2.SubClass;
public class TestSuperSub {
 
public TestSuperSub() {
super();
// TODO Auto-generated constructor stub
}
 
/**
 * @param args
 */
public static void main(String[] args) {
// TODO Auto-generated method stub
SuperClass superClass = new SubClass();
superClass.smile(1);
/*why this line gives comp. time error.
 as smile(int) has been overridden by SubClass from SuperClass. and SuperClass Reference refer to SubClass Object.Here Subclass promotes 
the visibility to public
*/
}
 
}
 

[Anton Uwe]

Well, for the compiler, "superClass" has no method "smile(..)" because "smile(..)" in SuperClass was defined to be protected and we are in a different package than SuperClass is in, and we are not in a class inheriting from SuperClass. So, the compiler doesn't "see" "smile(..)".