Why it is not overriding

Question

Hi,
I m puzzled by the output of :
public class MyClass2 {
private void f() {
System.out.println("private f()");
public static void main(String[] args) {
MyClass2 po = new Derived();
po.f();
class Derived extends MyClass2 {
public void f() {
System.out.println("public f()");
output: private f(); why it is happening...... when it is said that at runtime base class's ref chk the object that it is holding & executes its method ...ie; runtime polymorphism ...but in above case ...can any body tell why it is not happening.......?
Thanks in advance.....

Answer 1

Read the OPs question again: The method of the base class is private and the method of the subclass is public, not the other way around!
When you override the method, the signature must remain the same. You can change the access modifier but only to a less restricted one. That's what the OP did!
So you can't make a public method private. Correct!
But you could make a protected one private.Wrong! You could make a protected one public.
@OP: private members are only visible in the class it defines - not in subclasses. So the subclass would not know that there is a method with the same signature and that it overrides this method!
So what happens? If you redeclare a method in a subclass a method, which was private in the superclass, it hides the method of the superclass. Polymorphism does not apply when calling private methods!
public static void main(String[] args) {
  MyClass2 po1 = new MyClass2();
  po1.f(); //-> calls private method of MyClass2; can only be called from within MyClass2; no polymorphism!
  MyClass2 po2 = new Derived();
  po2.f(); //-> calls private method of MyClass2 because po2 is declared as MyClass2; can only be called from within MyClass2; no polymorphism!
  Derived po3 = new Derived();
  po.f(); //-> calls public method of Derived, which *hides* the method of MyClass2
  MyClass2 po4 = new Derived();
  ((Derived) po).f(); // -> po4 is declared as MyClass2 but we explicitly cast it to Derived, so the method of Derived gets called.
}Look up hiding for more information!
-Puce