Sunday, March 9, 2008

overriding vs field hiding in java and c++

[[Java precisely]] P40 summarizes

· In a non-static field access o.f, the field referred to is determined by the compile-time type of the object expression o
· In a non-static call to a non-private method o.m(), the method called is determined by the run-time class of the target object: the object to which o evaluates to

Say C.java extends B.java,

Q: if you only have an object o=new C(), how can you access f and m() declared in B.java?
A: With the exception below, you can’t access B::m(). The method call o.m() resolves at run time and always binds to C::m(). However, f is a different story. You can cast o to B and o.f would refer to B::f

A special context -- super.f and super.m() do give you access to parent’s members, but you can only use this syntax in C’s constructors or non-static methods, essentially in C.java source code.

I wonder what C++ does.. Here are some tidbits.

o.B::m() actually let’s you call parent’s m() via a subclass object. Also see Item 50 in [[eff c++]]

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