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How to not use casting to invoke the methods of a List of objects

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  How to not use casting to invoke the methods of a List of objects clusardi2k@aol.com - 2012-07-20 06:58 -0700
    Re: How to not use casting to invoke the methods of a List of objects markspace <-@.> - 2012-07-20 07:21 -0700
      Re: How to not use casting to invoke the methods of a List of objects clusardi2k@aol.com - 2012-07-20 08:09 -0700
    Re: How to not use casting to invoke the methods of a List of objects Joerg Meier <joergmmeier@arcor.de> - 2012-07-20 17:45 +0200
      Re: How to not use casting to invoke the methods of a List of objects Robert Klemme <shortcutter@googlemail.com> - 2012-07-20 18:03 +0200
        Re: How to not use casting to invoke the methods of a List of objects Joerg Meier <joergmmeier@arcor.de> - 2012-07-20 18:59 +0200
    Re: How to not use casting to invoke the methods of a List of objects Roedy Green <see_website@mindprod.com.invalid> - 2012-07-20 21:22 -0700
    Re: How to not use casting to invoke the methods of a List of objects Lew <noone@lewscanon.com> - 2012-07-21 23:34 -0700

#16146 — How to not use casting to invoke the methods of a List of objects

Below uses a List of objects of class Route. Class Route has public member variables (such as locationid) and public methods (such as get_locationid()). The below code is a first attempt at a way to obtain the value of locationid using casting. Question: What is the code to do it a better way.

((Route)objList.get(0)).locationid;
((Route)objList.get(1)).locationid;

The below start of replacement code fails because it skips through the list. There wasn't a good reason for me to finish the code! The loop can't even iterate the required number of loops.

        Iterator <Route> it = objList.iterator();
 
        int size = objList.size();

        for (int i = 0;i < size; i++)
        {
           it.next();
        }

Thank you,

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#16147

On 7/20/2012 6:58 AM, clusardi2k@aol.com wrote:

> The
> loop can't even iterate the required number of loops.


You might want to be more clear about what is really failing here. 
Iterator works, so the problem must be somewhere else in the code, which 
you are not showing.


>
 >          Iterator <Route> it = objList.iterator();
 >
 >          int size = objList.size();
 >
 >          for (int i = 0;i < size; i++)
 >          {

Maybe you could try this:

 >             Route r =  it.next();
 >          }


But in general the for-each construct works better

   for( Route r : objList ) {
     r. ...
   }

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#16150

> On Friday, July 20, 2012 10:21:56 AM UTC-4, markspace wrote:
>  > On 7/20/2012 6:58 AM, me wrote:
>  >           for (int i = 0;i < size; i++)
>  >           {
> 
> Maybe you could try this:
> 
>  >             Route r =  it.next();
>  >           }
> 

This works when I don't use the debugger to step through, thanks!

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#16152

On Fri, 20 Jul 2012 06:58:49 -0700 (PDT), clusardi2k@aol.com wrote:

> The below start of replacement code fails because it skips through the list. There wasn't a good reason for me to finish the code! The loop can't even iterate the required number of loops.

>         Iterator <Route> it = objList.iterator();

>         int size = objList.size();

>         for (int i = 0;i < size; i++)
>         {
>            it.next();
>         }

That is not really how you use iterators. Proper way:

Iterator <Route> it = objList.iterator();

while (it.hasNext()) {
	it.next();
}

Liebe Gruesse,
		Joerg

-- 
Ich lese meine Emails nicht, replies to Email bleiben also leider
ungelesen.

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#16153

On 20.07.2012 17:45, Joerg Meier wrote:
> On Fri, 20 Jul 2012 06:58:49 -0700 (PDT), clusardi2k@aol.com wrote:
>
>> The below start of replacement code fails because it skips through the list. There wasn't a good reason for me to finish the code! The loop can't even iterate the required number of loops.
>
>>          Iterator <Route> it = objList.iterator();
>
>>          int size = objList.size();
>
>>          for (int i = 0;i < size; i++)
>>          {
>>             it.next();
>>          }
>
> That is not really how you use iterators. Proper way:
>
> Iterator <Route> it = objList.iterator();
>
> while (it.hasNext()) {
> 	it.next();
> }

In 2012 I'd rather say the proper way for a simple iteration (i.e. 
without removing elements or such) is

for (final Route r : objList) {
   // camel case and accessor added:
   System.out.println(r.getLocationId());
}

Assuming objList is assignment compatible to Iterable<Route>.  We 
haven't seen the declaration in the original posting though so we can 
only speculate.

I do have to agree that the original question was quite a bit dark.

Cheers

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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#16156

On Fri, 20 Jul 2012 18:03:08 +0200, Robert Klemme wrote:

> In 2012 I'd rather say the proper way for a simple iteration (i.e. 
> without removing elements or such) is

> for (final Route r : objList) { [...]

I agree that the enhanced for loop is preferrable for cases without
structural changes to the list. Blame tunnel vision ;)

Liebe Gruesse,
		Joerg

-- 
Ich lese meine Emails nicht, replies to Email bleiben also leider
ungelesen.

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#16176

On Fri, 20 Jul 2012 06:58:49 -0700 (PDT), clusardi2k@aol.com wrote,
quoted or indirectly quoted someone who said :

>Below uses a List of objects of class Route. Class Route has public member =
>variables (such as locationid) and public methods (such as get_locationid()=
>). The below code is a first attempt at a way to obtain the value of locati=
>onid using casting. Question: What is the code to do it a better way.

see http://mindprod.com/jgloss/generics.html

Generics let you tell the compiler what types you are hiding in your
collections so it can do the casting for you.
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
The greatest shortcoming of the human race is our inability to understand the exponential function. 
 ~ Dr. Albert A. Bartlett (born: 1923-03-21 age: 89)
http://www.youtube.com/watch?v=F-QA2rkpBSY

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#16206

On 07/20/2012 06:58 AM, clusardi2k@aol.com wrote:
> Below uses a List of objects of class Route. Class Route has public member

Public variables are frowned upon in Java. That doesn't mean never use them, 
but it does make me wonder why you also defined an accessor method.

> variables (such as locationid) and public methods (such as get_locationid()).

You should follow the Java naming conventions: locationId and getLocationId(). 
Camel case. No underscores.

Don't describe your code. That's all but useless. Show your code.

http://sscce.org/

> The below code is a first attempt at a way to obtain the value of locationid
> using casting. Question: What is the code to do it a better way.

In addition to what everyone else has said
> ((Route)objList.get(0)).locationid;

'objList' is a bad name. You have a collection of 'Route's, right? So your 
variable should be 'routes'.

> ((Route)objList.get(1)).locationid;
>

Why are you casting at all?

   Route route = routes.get(0);

You did declare your list as a 'List<Route>', of course, right?

> The below start of replacement code fails because it skips through the list. There wasn't a good reason for me to finish the code! The loop can't even iterate the required number of loops.
>
>          Iterator <Route> it = objList.iterator();

Indent enough?

>          int size = objList.size();
>
>          for (int i = 0;i < size; i++)
>          {
>             it.next();
>          }

You shouldn't use both indexes and iterators in the same loop. Stick with one 
or another for any given loop.

You should never use an iterator 'next()' without checking 'hasNext()' first.

You often can, and therefore in those cases should, use the for-each loop, as 
others have already said:

   for (Route route : routes)
   {
     doSomethingWith(route);
   }

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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