Re: How to create an object of a given class NAME?

From:

"Karl Uppiano" <karl.uppiano@verizon.net>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 30 Nov 2006 20:52:26 GMT

Message-ID:

<ewHbh.12275$gJ1.3489@trndny09>

"Miguel Farah" <miguel@farah.cl> wrote in message
news:1164918608.494658.51630@h54g2000cwb.googlegroups.com...

I got the following piece of code:

   static private Idiom determineIdiom(Locale region) {
       if (region==null) region=DEFAULT_REGION;
       String language=region.getLanguage();
       if (language==null) language=DEFAULT_LENGUAJE;

       Idiom myIdiom=null;
       if (language.equals("es")) { myIdiom=(Idiom)new
Idiom_es();
       } else if (language.equals("en")) { myIdiom=(Idiom)new
Idiom_en();
       } else if (language.equals("ca")) { myIdiom=(Idiom)new
Idiom_ca();
       } else if (language.equals("fr")) { myIdiom=(Idiom)new
Idiom_fr();
       } else {
           myIdiom=(Idiom)new Idiom_es(); //default
       }
       return myIdiom;
   }

All the Idiom_* classes extend Idiom, which in turn implements an
interface. If I want to add support for a new language (say, finnish),
I
have to write a Idiom_fi class AND I have to put a new if sentence in
this method:

       } else if (language.equals("fi")) { myIdiom=(Idiom)new
Idiom_fi();

I'd like to get rid of the second requirement, and for that I'd need to
be able to
compose the name of the class I want to instance, sorta like this:

myIdiom=(Idiom)new {{"Idiom_"+language}}();

I'm not sure if this can be done in Java. Can it?

Thanks in advance.

You could use reflection to avoid using hard-coded class names. Then to
support a new language, you would need to write a new class, but plug it in
using a resource bundle to map the language to the class name, e.g.,

in a resource properties file (e.g.,
..../my/idiom/package/Resources.properties),

    en_us=my.idiom.package.Idiom_en
    de_de=my.idiom.package.Idiom_de

etc. Obviously, there are details, such as variants (e.g., en_us_cajun) that
you might have to deal with.

In your code, instead of a bunch of if statements, you would do something
like this (some details, such as exception handlers, omitted - treat this as
pseudo code):

    ResourceBundle resources =
ResourceBundle.getBundle("my.idiom.package.Resources");
    String idiomClassName = resources.getString(region.getLanguage());
    Class idiomClass = Class.forName(idiomClassName);
    Idiom myIdiom = (Idiom)idiomClass.newInstance();

    return(myIdiom);

Reflection is a very good way to accomplish plug-ins.