Question about "data hiding" OOP paradigm issue

[t_bigford@xxxxxxxxx (Tom Bigford)]

Hi Cedric - Thanks - I don't know if you answered
Sordini's question - but you answered one of mine
(unasked) - Now i see how you handle the idea of const
parameters in java...

Thanks - Tom

--- Cedric Beust <Cedric.Beust@xxxxxxx> wrote:
> > From: Sordini Emmanuele
> [mailto:Sordini.Emmanuele@xxxxxxxxxxxxxx]
> 
> > 1)	When I call mc.doSomething() the state of mc is
> changed, and so is
> > the state of theObject. Or am I wrong? Feeding the
> setter with a reference
> > to mc is quite performance-effective, but clearly
> breaks OOP visibility
> > rules.
> > 2)	If, on the other hand, I passed the setter a
> copy of mc, that would
> > ensure respecting the rule but would generate some
> memory and performance
> > overhead, which is not advisable given Java's
> generally poor scores.
> >
> > Anybody have any opinions / hints?
> 
> It's impossible to give a general recommendation, it
> really depends on the
> semantics of your class. You correctly identified
> the trade-offs :
> 
> - pass by reference : efficient, but possibility for
> the object to be modified
> with side-effects
> - pass by value (clone) : no side-effects, but
> probably unnecessarily slow
> 
> The typical way to deal with this problem is the
> Immutable idiom. Break your
> class in two parts, one being read-only and which
> contains exclusively "const
> member functions" to use C++ terminology :
> 
> class ConstMyClass {
>   public Object getValue() { ...}
> };
> 
> class MyClass extends ConstMyClass {
>   public setValue(Object o) { ... }
> }
> 
> Then, just pick the appropriate type in your
> method's signatures.
> 
> Does this answer your question ?
> 
> --
> Cedric
> http://beust.com/cedric
> 
> 
> 
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> 
> 

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