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From Gilles Sadowski <gil...@harfang.homelinux.org>
Subject Re: [Math] Confusing (?) use of "getInstance()" in formatting classes
Date Tue, 26 Jul 2011 13:40:55 GMT
On Tue, Jul 26, 2011 at 02:00:39PM +0100, sebb wrote:
> On 26 July 2011 13:19, Gilles Sadowski <gilles@harfang.homelinux.org> wrote:
> > Hi.
> >
> > [This is related to issue MATH-622.]
> >
> > Looking at the "CompositeFormat" and "RealVectorFormat", I notice an unusual
> > use of the "getInstance" method name. Unless I'm mistaken, "getInstance" is
> > most often used when the object stores a reference to a singleton. And in
> > those class, this does not seem to be the case: When I write
> > ---
> >  RealVectorFormat.getInstance().getFormat().setMaximumFractionDigits(6);
> > ---
> > the output is unaffected, the default being to display 2 fraction digits),
> > which is not suitable for debugging.
> >
> > I think that there should be a way to modify at once all outputs formatted
> > through "CompositeFormat", i.e. an actual singleton instance of "NumberFormat"
> > that is used by all "default" formatting.
> >
> > Do you agree? Any caveats?
> 
> The singleton will need to be thread-safe.
> 
> A mutable singleton is thread-hostile (*), so if this approach is
> taken, the Javadoc need to make this very clear.

I don't particularly like it either but do you see another way?

Yes, there is: To not use CM's formatting in the definition of the
"toString()" methods and/or overload them as
---
  public String toString(NumberFormat fmt) { /* ... */ }
---
Then when debugging, one will be able to fairly easily write:
---
   RealVector v = new ArrayRealVector(new double[] {1.2345678, 2.3456789});
   System.out.println("v=" + v.toString(CompositeFormat.getDefaultNumberFormat(8)));
---

> (*) Thread A sets the digit count, thread B sets it differently;
> thread A may not get the desired digit count.

For debugging, the expectation is that the user sets it once, at the
top-level ("main"); so that will not be a problem usually.


Gilles

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