mock exam problem

[Honggui Li]

hello, everyone:
I am taking a mock exam ,i got a problem with one of the mock exam questions.
Let's see the following code:
class Base {
private void amethod(int iBase){
System.out.println("Base.amethod");
}
}
class Sub extends Base{
public static void main(String a[ ]){
Sub s = new Sub();
int iBase =0;
s.amethod(iBase);
}
public void amethod (int iSub){
System.out.println("Sub.amethod");
}
}
the answer is :Output of "Sub.amethod"
I disagree with the answer. My opinion is : the amethod in the superclass is a private method, it can't be seen in the subclass. maybe this code works fine. but the amethod in the subclass isn't a version of an overriding method.
I will try to run the code tonight. I just want to know if we can override a private method from superclass or not?
Hope someone can help me figure out that.
thanks a lot.
honggui

[Guoqiao Sun]

Hi, Honggui, we cannot override method with private access modifier from super class. If the derived class happens to have a method with the same singiture with that private method, it is just a normal method in the derived, has nothing to do with overriding.
In fact, the code you provide should either be

Sub s = new Sub();
s.amethod(100);

or

Base s = new Sub();
((Sub)s).amethod(100);

The following will not compile:

Base s = new Sub();
s.amethod(100);

since the amethod binding at compile time will find that amethod in Base has private access and fail it.
Hope it helps.
Guoqiao

Originally posted by Honggui Li:

[Honggui Li]

Hello,guoqiao:
Thank you for your kindly help. I learned a lot from your reply.
Acturally, I am confused with your last code. let's say
Base b = new Sub();
b.amethod(100);
In this case, in my opinion, it will use the amethod() in the Sub class, since the actural object type of b is Sub, the reference type of b is Base, so, i think java will decide which method will be used based upon the object type.
I haven't tried that, let's compile and see what will happen.
By the way, when i do the mock exam for programmer test, i always can't figure out the compile time error and runtime error. I know there is something wrong with the code, but sometimes it is very difficult to choose the compile time error or runtime error.
If u have any experience in this field, hope u can give me some hints.
Anyone who knows where i can find some useful resources about this topic can feel free to reply to me.
Thanks a lot.
Honggui