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method conversion question  RSS feed

 
Veena Pointi
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The following question is from Dan's mock exam.

I thought static void m(A x, C y) method is the more specific one.So my expected answer was AC.
It gives compiler error.why?Isn't static void m(A x,C y) method most specific one?
Thanks
Veena
 
John Zoetebier
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The compiler says:

reference to m is ambiguous,
both method m(B,B) in C
and method m(A,C) in C match

1. Class C extends B => C IS_A B
2. Class B extends A => B IS_A A
And because operator IS_A is transitief it follows from 1 and 2 that: C IS_A A
We now know that object c can be passed to m(B,B) or m(A,C)
Can (B,B) be passed on to (A,C): no, because B not IS_A C
Can (A,C) be passed on to (B,B): no, because A not IS_A B
Conclusion: m(B,B) is not more specific than m(A,C)
BTW: all methods are in 1 class.
If methods from a superclass class are overloaded the rules involve the classes as well.
See other posting for this subject.
 
Veena Pointi
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Thanks John,I got it .
[ April 29, 2003: Message edited by: Veena Point ]
 
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