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Re: a question about factory method

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On 18.12.2014 14:57, John wrote:

 > I am reading a very good web site
 > http://www.javapractices.com/topic/TopicAction.do?Id=21

> The code uses a private constructor and the factory method. I also
> notice this class is an immutable class. If I write this class, I
> would simply have a public constructor, like:
> Could you explain to me why their code is better than mine? If
> theirs  is singleton, I would agree. But in this case, it does not make sense
> for using singleton. The only thing I can think of is using their code
> is more like following a trend, e.g. String.valueOf(xxx).

By using this method authors of that class gain a lot of freedom, notably

  - regarding the type of return value
  - regarding the point in time when an instance will be created

For example: it may make sense to have different classes for the cases 
that imaginary part is 0 and is not 0.

Then, it may be later decided to optimize allocation of Complex 
instances and use something like an internal pool (e.g. similar for 
small Integer values).  If you use a constructor there will be a new 
instance _every time_.

By providing the factory method the API for obtaining Complex instances 
can stay the same while internally more changes can be done.

Btw. these properties are mentioned at the top of the page that you linked.

> I guess most people will do what I do here.

Probably.  But that does not mean that this solution is better.

Btw. I wonder why they did not make member fields final.  Also it seems, 
Complex could be Serializable.

Kind regards

	robert



-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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Thread

a question about factory method John <xsli2@yahoo.com> - 2014-12-18 05:57 -0800
  Re: a question about factory method Robert Klemme <shortcutter@googlemail.com> - 2014-12-18 15:28 +0100
  Re: a question about factory method Silvio <silvio@internet.com> - 2014-12-18 15:43 +0100
  Re: a question about factory method Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-12-18 10:37 -0500
    Re: a question about factory method John <xsli2@yahoo.com> - 2014-12-18 08:04 -0800
      Re: a question about factory method Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-12-18 12:04 -0500
        Re: a question about factory method John <xsli2@yahoo.com> - 2014-12-18 10:43 -0800
          Re: a question about factory method Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-12-18 14:24 -0500
            Re: a question about factory method Robert Klemme <shortcutter@googlemail.com> - 2014-12-19 01:39 +0100
  Re: a question about factory method Roedy Green <see_website@mindprod.com.invalid> - 2014-12-18 13:43 -0800

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