Re: Chained call pattern with inheritance, polymorphism and generics...

From:
Piotr Kobzda <pikob@gazeta.pl>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 29 Sep 2007 08:57:36 +0200
Message-ID:
<fdkt10$t68$1@inews.gazeta.pl>
Daniel Pitts wrote:

What's wrong then with pattern presented by Daniel to achieve that?

I can't make any sense of it.


What if I changed it to this:

public class BaseBuilder<T> {
    private String something;
    public T something(String something) {
       this.something = something;
       return getChainTarget();


I guess, it should return getChainLink() here.

    }

    protected abstract T getChainLink();
}

public class SpecificBuilder extends BaseBuilder<SpecificBuilder> {

    private String other;

    public SpecificBuilder other(String other) {
        this.other = other;
    }

    protected SpecificBuilder getChainLink() {
     return this;
   }
}

SpecificBuilder b = new
SpecificBuilder().something("Hello").other("World!");

This works since something() returns T, which in SpecificBuilder IS
SpecificBuilder.

The problem with my solution is that I can't have:


Of course you can:

class MoreSpecificBuilder extends SpecificBuilder {
    public void doMore() {
    }
    protected MoreSpecificBuilder getChainLink() {
     return this;
   }


      @Override
      public MoreSpecificBuilder something(String something) {
          super.something(something);
          return getChainTarget();
      }

      @Override
      public MoreSpecificBuilder other(String other) {
          super.other();
          return getChainLink();
      }

}

new MoreSpecificBuilder().something("hello").doMore(); // whoops!


Try it now! :-)

piotr

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