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

From:

Daniel Pitts <googlegroupie@coloraura.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 29 Sep 2007 19:02:23 -0000

Message-ID:

<1191092543.448935.106890@w3g2000hsg.googlegroups.com>

On Sep 28, 11:57 pm, Piotr Kobzda <pi...@gazeta.pl> wrote:

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

The point is, I shouldn't have to delegate to super just to return the
same reference as a different type.

While that IS currently the case, I wish it werent.