[Bluej-discuss] Excercise 4.25 review please

[David J. Barnes]

JD,

Chaining together method calls like that is a relatively rare occurrence, but the possibility is worth knowing about. When explaining it to students it is probably worth breaking it down into stages.
Instead of writing:

    highestBid.getBidder ().getName();

we can make use of an additional local variable:

    Person winner = highestBid.getBidder();

and then make the call:

    winner.getName()

Because the getBidder call returns an object reference, there is nothing to stop us in Java making the call directly on the return value. When a local variable is only being used as a staging post in this way it is sometimes omitted.

Hope that helps,

David

On Sun, 18 Jun 2006 16:00:20 -0700
JD <dnaltrop at gmail.com> wrote:

> Hi Rob -
> 
> Thanks for the reply.  In the end I I knew I was making an external method
> call...It just that I didnt know you could call a local object reference
> highestBid that calls another object reference getBidder() in an external
> class Bid that calls another object reference bidder  in another external
> class Person that FINALLY calls a real method getName that returns the
> bidders person name....whew!.... I hope this book explores more examples of
> these chained external method calls as I am sure they are common to use.
> 
> On 6/18/06, RDP <robdepasquale at msn.com> wrote:
> >
> >  JD,
> >
> > You've just discovered the "eternal method call" using DOT NOTATION
> > (contrast "internal method call").
> >
> > See Page 67 in the text book which explains calling methods of other
> > objects.
> >
> > details += " sold for $" + highestBid.getValue() + "  to: "  +
> > highestBid.getBidder ().getName();
> >
> > Your code above is what did it.
> >
> > Unfortunately, I think the text does not explain nor present more examples
> > of external method calls using dot notation.
> >
> > Hey good luck!!
> >
> > Best regards,
> >
> > Rob DePasquale
> > Bon Vivant!
> >
> > ----- Original Message -----
> > *From:* JD <dnaltrop at gmail.com>
> > *To:* bluej-discuss at bluej.org
> > *Sent:* Sunday, June 18, 2006 1:36 PM
> > *Subject:* [Bluej-discuss] Excercise 4.25 review please
> >
> > Hi all!
> >
> > Please review and comment on my solution for Exercise 4.24.  I have a
> > question at the bottom of this email as well.
> >
> > Auction Class:
> >
> >      /**
> >      * Close Lot
> >      * @return Close lots
> >      */
> >
> >     public void closeAuction()
> >     {
> >         Iterator it = lots.iterator();
> >         while(it.hasNext()) {
> >             Lot lot = (Lot) it.next();
> >             System.out.println(lot.closeLot());
> >         }
> >     }
> >
> >
> > Lot Class:
> >
> >     /**
> >      * @return A string representation of this lot's details.
> >      */
> >     public String closeLot()
> >     {
> >         String details = number + ": " + description;
> >         if(highestBid != null) {
> >             details += " sold for $" + highestBid.getValue() + "  to: "
> > +  highestBid.getBidder ().getName();
> >         }
> >         else {
> >             details += "    (No bid)";
> >         }
> >         return details;
> >     }
> >
> >
> > Output:
> >
> > 1: Car sold for $3432  to: Carl
> >
> > 2: Cat    (No bid)
> >
> >
> > Question:
> >
> > The following line of code gave me the most grief until I got it working.
> >
> > highestBid.getBidder().getName();
> >
> > It is an object reference to a method to another object to a method within
> > the object referenced by the getBidder() method!?!?!?  It works.  But what
> > the heck did I create here?  What is it called?  Have we covered this type
> > of construction in the book yet and I missed it?
> >
> >  ------------------------------
> >
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