Re: question
Daniel Moyne wrote:
Peter Fourneau wrote:
On Sep 26, 11:57 am, Daniel Moyne <dmo...@tiscali.fr> wrote:
Peter F wrote:
On Sep 25, 8:17 pm, Daniel Moyne <dmo...@tiscali.fr> wrote:
I am building a map with the key as an integer and a list of string as
the value ; basically this is the stripped code :
import java.util.Map;
import java.util.HashMap;
import java.util.TreeMap;
import java.util.ArrayList;
public class map {
public static void main(String args[]) {
ArrayList<String>clonableDataList=new ArrayList<String>();
Map<Integer,ArrayList<String>>clonableDataMap= new
HashMap<Integer,ArrayList<String>>();
for (int i=0;i<3;i++) {
clonableDataList.removeAll(clonableDataList);
clonableDataList.add(Integer.toString(i));
clonableDataList.add(Integer.toString(i+1));
clonableDataMap.put(i,clonableDataList);
System.out.println("key="+Integer.toString(i)+"list="+clonableDataList+"**");>>
}
for (Map.Entry <Integer,ArrayList<String>>
entry :clonableDataMap.entrySet()) {
ArrayList<String>aa=new ArrayList<String>(entry.getValue());
System.out.println("key="+Integer.toString(entry.getKey())+"list="+entry.getValue()+"**");
}
}}
when I run the code I get this :
key=0list=[0, 1]**
key=1list=[1, 2]**
key=2list=[2, 3]**
[2, 3]
key=2list=[2, 3]**
[2, 3]
key=1list=[2, 3]**
[2, 3]
key=0list=[2, 3]**
so apparently I get all the time the same list "2, 3" for all the the
different keys when printing my map ; what is wrong ?
Thanks.
--
Daniel Moyne
(Nulix)---------------------------------------------------------
Distribution : Ubuntu Feisty \\|||// Machine : x86_64
kernel 2.6.20-16-generic / --- \ ATI Radeon X300
KDE 3.5.7 (' o-o ')
----------------------------------------oOO-(_)-OOo--------------------------
Nothing is wrong, this is normal behaviour...you're always adding the
same clonableDataList to your map, and each new iteration, you remove
all the elements from the clonableDataList. Only the last iteration
(with key 2 and values 2,3) are kept.
You need to create a new clonalbeDataList each iteration, so that each
key in you map will have his own clonableDataList.
I suggest that you replace
clonableDataList.removeAll(clonableDataList); with
clonableDataList= new ArrayList<String>();
Regards
Peter
thanks so I was expecting by recycling the same clonableDataList with :
clonableDataList.removeAll(clonableDataList);
to correctly clean the list before adding fresh new elements I will use
instead :
clonableDataList= new ArrayList<String>();
but I still do not understand what this line is actually doing in the
first loop ?
Daniel.
--
Daniel Moyne
(Nulix)---------------------------------------------------------
Distribution : Ubuntu Feisty \\|||// Machine : x86_64
kernel 2.6.20-16-generic / --- \ ATI Radeon X300
KDE 3.5.7 (' o-o ')
----------------------------------------oOO-(_)-OOo--------------------------
It's indeed better to create a new clonableDataList before going to
the next loop and not as first action of a new loop.
public class map {
public static void main(String args[]) {
ArrayList<String>clonableDataList=new ArrayList<String>();
Map<Integer,ArrayList<String>>clonableDataMap= new
HashMap<Integer,ArrayList<String>>();
for (int i=0;i<3;i++) {
clonableDataList.add(Integer.toString(i));
clonableDataList.add(Integer.toString(i+1));
clonableDataMap.put(i,clonableDataList);
clonableDataList=new ArrayList<String>();
}
}
}
so in this case, we don't create a unnecessary clonableDataList in the
first loop.
Yes Peter what you suggest works but also thoses slightly different versions
work as well :
(a)
import java.util.Map;
import java.util.HashMap;
import java.util.TreeMap;
import java.util.ArrayList;
public class map {
public static void main(String args[]) {
ArrayList<String>clonableDataList();
Map<Integer,ArrayList<String>>clonableDataMap=new
HashMap<Integer,ArrayList<String>>();
for (int i=0;i<3;i++) {
clonableDataList.add(Integer.toString(i));
clonableDataList.add(Integer.toString(i+1));
clonableDataMap.put(i,clonableDataList);
clonableDataList=new ArrayList<String>();
}
}
}
You should use whitespace, e.g., between "ArrayList<String>" and the variable
(if that is what it is) "clonableDataList" being declared. Also, that
particular line will not compile, as it looks sort of like a declaration and
sort of like a method invocation. It's not legal Java.
Why do you convert the integers to String instead of using them (boxed) in the
list?
Someone else pointed out that "map" is not a good name for a class. It is
confusingly similar to a standard API class, and it doesn't follow the
conventions.
(b)
import java.util.Map;
import java.util.HashMap;
import java.util.TreeMap;
import java.util.ArrayList;
public class map {
public static void main(String args[]) {
ArrayList<String>clonableDataList;
Map<Integer,ArrayList<String>>clonableDataMap=new
HashMap<Integer,ArrayList<String>>();
for (int i=0;i<3;i++) {
clonableDataList=new ArrayList<String>();
clonableDataList.add(Integer.toString(i));
clonableDataList.add(Integer.toString(i+1));
clonableDataMap.put(i,clonableDataList);
}
}
}
This one looks much more normal.
regarding the put action on the map adding all the time the pointer to the
list and not the modified content of this very same list as I thought.
All non-primitive variables are simply references to an object. You can also
usually pretend that primitive variables are equivalent to references to their
respective wrapper-object values. (This last is /very/ loose but often useful.)
--
Lew