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

Discussion in 'Java' started by clusardi2k@aol.com, Jul 20, 2012.

  1. Guest

    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 eveniterate 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,
    , Jul 20, 2012
    #1
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  2. markspace Guest

    On 7/20/2012 6:58 AM, 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. ...
    }
    markspace, Jul 20, 2012
    #2
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  3. Guest

    > 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 &lt; size; i++)
    > > {

    >
    > Maybe you could try this:
    >
    > > Route r = it.next();
    > > }

    >


    This works when I don't use the debugger to step through, thanks!
    , Jul 20, 2012
    #3
  4. Joerg Meier Guest

    On Fri, 20 Jul 2012 06:58:49 -0700 (PDT), 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.
    Joerg Meier, Jul 20, 2012
    #4
  5. On 20.07.2012 17:45, Joerg Meier wrote:
    > On Fri, 20 Jul 2012 06:58:49 -0700 (PDT), 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/
    Robert Klemme, Jul 20, 2012
    #5
  6. Joerg Meier Guest

    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.
    Joerg Meier, Jul 20, 2012
    #6
  7. Roedy Green Guest

    On Fri, 20 Jul 2012 06:58:49 -0700 (PDT), 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
    Roedy Green, Jul 21, 2012
    #7
  8. Lew Guest

    On 07/20/2012 06:58 AM, 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
    Lew, Jul 22, 2012
    #8
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