Re: Instantiate an abstract class

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.help

Date:

Tue, 05 Apr 2011 15:09:51 -0700

Message-ID:

<b4GdnUdhF-OlDgbQnZ2dnUVZ_gSdnZ2d@earthlink.com>

On 4/5/2011 2:54 PM, Rob McDonald wrote:
....

Most of my online searches had lead down the reflection path and I
quickly got myself wrapped around the axle. I'm going to go with the
above implementation, but I am curious about how it could be made to
work the other way.

....

Obviously, a real implementation would handle the exceptions for a
subclass that does not have an accessible parameterless constructor, but
this should give you an idea. The advantage of this approach is that you
only need to require each subclass to have an accessible parameterless
constructor.

public abstract class AFoo {

   private AFoo getNewInstance() throws InstantiationException,
       IllegalAccessException {
     return (AFoo) getClass().newInstance();
   }

   public static void main(String[] args) throws InstantiationException,
       IllegalAccessException {
     AFoo bob = new Bob();
     AFoo bobExtra = bob.getNewInstance();
     System.out.println(bobExtra.getClass());

     AFoo fred = new Fred();
     AFoo fredExtra = fred.getNewInstance();
     System.out.println(fredExtra.getClass());
   }
}

class Bob extends AFoo {
}

class Fred extends AFoo {
}