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

C

clusardi2k

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,
 
M

markspace

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. ...
}
 
J

Joerg Meier

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
 
R

Robert Klemme

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
 
J

Joerg Meier

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
 
R

Roedy Green

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)
 
L

Lew

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 said:
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);
}
 

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