Inheritance Confusion

[Niral Trivedi]

All,
Found quesiton on Dan Chisholm's Topic specific exam.
<pre>
class R {
private void printS1(){System.out.print("R.printS1 ");}
protected void printS2() {System.out.print("R.printS2 ");}
protected void printS1S2(){printS1();printS2();}
}
class S extends R {
private void printS1(){System.out.print("S.printS1 ");}
protected void printS2(){System.out.print("S.printS2 ");}
public static void main(String[] args) {
new S().printS1S2();
}
}
</pre>
It says answers is 'Prints: R.printS1 S.printS2'
I couldn't understand explanation given for that answers on that site. So, can somebody explain?
Thanks a bunch in advance.
Niral

[nupur dhawan]

<pre>
class R {
private void printS1(){System.out.print("R.printS1 ");}
protected void printS2() {System.out.print("R.printS2 ");}
protected void printS1S2(){printS1();printS2();}
}
class S extends R {
private void printS1(){System.out.print("S.printS1 ");}
protected void printS2(){System.out.print("S.printS2 ");}
public static void main(String[] args) {
new S().printS1S2();
}
}
</pre>
It says answers is 'Prints: R.printS1 S.printS2'

Niral,
new S().printS1S2(); // invokes the method printS1S2() of class R.
printS1() of that method invokes private
method printS1() of class R.(private methods are not inherited, so the private method printS1() in class S is a different method .)
printS2() invokes the overriding method of class S .
Thus, the output:R.printS1 S.printS2
Hope this helps .

[Dan Chisholm]

Niral,
You're right. The explanation given in the exam for that answer was not very good. I updated the XML source document as follows.

Method R.printS1 is private and therefore is not inherited by class S and is not overridden by method S.printS1. In contrast, method R.printS2 is protected and therefore is inherited by class S and is overridden by method S.printS2. R.printS1S2 therefore calls the R.printS1
and S.printS2 methods.

I'll update the html and the web site soon.

[Niral Trivedi]

Thank you guys.. that really helped..

but I've read in book 'Complete Java 2 Certification Study Guide' that...

A private method may be overridden by a private, default,protected or public method.

So, isn't that the case in our example?? printS1 method is private in Class R and has been overridden by private printS1 method in class S. So, what is the difference in book statement and here?
sorry but I need to clear my doubts.
Thanks again..
Niral

[Anthony Villanueva]

See JLS 8.4.6.3

Note that a private method cannot be hidden or overridden in the technical sense of those terms. This means that a subclass can declare a method with the same signature as a private method in one of its superclasses, and there is no requirement that the return type or throws clause of such a method bear any relationship to those of the private method in the superclass.