RE: the benefits of immutability

["Kevin S. Millikin" <address@hidden>]

On Tuesday, August 19, 2003 8:37 AM, Perry E. Metzger 
[SMTP:perry@piermont.com] wrote:
>
> Vadim Nasardinov <el-vadimo@comcast.net> writes:
> > Perry E. Metzger wrote:
> >  > His so-called "reason" doesn't explain why StringBuffer is 
final,
> >  > too, in any case.
> >
> > That is correct.  I have not made any comments on why StringBuffer
> > is
> > final.  What would be the relevance of such a discussion to the
> > issue
> > at hand?
>
> You explicitly claimed that String was final so that strings could be
> immutable. You then carefully ignored it when it was pointed out
> StringBuffer is final, and yet is mutable.

I believe that Vadim was claiming that *if* java.lang.String were not 
final, *then* one could not guarantee that all objects of type 
java.lang.String were immutable.

That is, either a class is final or it cannot be guaranteed to be 
immutable.

An example of a class that is final *and* mutable is not a 
counterexample, for it certainly satisfies the disjunction "final or 
not guaranteed immutable".

A counterexample would consist of a class that was both "not final" and 
"guaranteed to be immutable".  StringBuffer does appear largely 
irrelevant, here.