[341] in java-interest
Re: confusion over which method is invoked
daemon@ATHENA.MIT.EDU (Andrew Wason)
Thu Jun 15 13:54:14 1995
To: java-interest@java.Eng.Sun.COM
In-Reply-To: Message from David.Geary@central.sun.com (David Geary)
of "Thu, 15 Jun 95 09:56:52 +0700." <9506151556.AA02072@trilby.Central.Sun.COM>
Date: Thu, 15 Jun 95 13:34:08 -0400
From: Andrew Wason <aw@bae.bellcore.com>
David.Geary@central.sun.com (David Geary) writes:
> > > class AccessTest {
> > > public static void main(String argv[]) {
> > > ClassB b = new ClassB();
> > > ClassA a = b;
> > > a.printname();
> >
> > Because printname is a virtual method, it will actually
> > call the printname in ClassB.
>
> In C++, it makes no difference whether printname() is virtual or not.
> a.printname() should invoke A::printname(), since a is an object of class A.
In Java the variables 'a' and 'b' are really references, so 'a =
b' just makes 'a' reference the object referenced by 'b'. And
since printname() is virtual, it's invoked in ClassB.
In C++ the above code might look like this (using pointers):
ClassB *b = new ClassB();
ClassA *a = b;
a->printname();
and so ClassB::printname() is invoked.
Andrew
_______________________________________________________________________________
Andrew Wason Bell Communications Research
aw@bae.bellcore.com Piscataway, NJ
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