Re: T copy()

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 12 Dec 2009 17:56:37 -0500

Message-ID:

<hg1735$5lu$1@news.albasani.net>

Daniel Pitts wrote:

This might be a better approach:
public abstract class LinearOperator {
   Element argument;

   /**
     * Derived classes will return new Self(newArgument);
     * Replacing Self appropriately
     */
   public abstract LinearOperator sameOperator(Element newArgument);

   public Element distribute() {
       return argument.distribute(this);
   }
}

public class Element {

Many times it'd be better to have this 'Element' type as an interface.

   public Element distribute(LinearOperator lo) {
      throw new UnsupportedOperation(
          "Can not distribute an element of type " + getClass());
   }
}

public class Sum extends Element {
   // assuming a,b defined.
   @Override
   public Sum distribute(LinearOperator lo) {
       return new Sum(lo.sameOperator(a), lo.sameOperator(b));
   }
}

This is one of many ways you can do that.

The main point is that instead of making LinearOperator or Element be aware of
their subtypes, you're using polymorphism to resolve the exact action to take.
This is good programming.

--
Lew