Problem While Removing Element From List

[Gowher Naik]

class ListTest{
public static void main(String args[]){
List<String> l=new ArrayList<String>();
l.add("0");
l.add("1");
l.add("2");
l.add("3");
               
for(int i=0;i<l.size();i++){
l.remove(i);
}
for(int i=0;i<l.size();i++){
System.out.println(l.get(i));
}
}
}

output is-> 1 3
i am not able to understand why 1 and 3 is not removed from List.

[wise owen]

while (l.size()!=0)
   l.remove(0);

Because i add 1 in each loop.
1) i=0, remove "0"; The "1" element move to index 0 and l.size()=3
2) i=1, remove "2"; The "3" element move to index 1 and l.size()=2
3) i=2, exit loop because the condition of "i<l.size();"
[ August 04, 2006: Message edited by: wise owen ]

[Paul Michael]

wise is correct. try to remove the elements from the list backwards.
using highest indeces first. that way, it won't mess up your for loop.

[Gautam Malik]

try out this:

////////////////////////////////////////////////////////////////////////////
import java.util.*;
class test
{
public static void main(String args[]){
List<String> l=new ArrayList<String>();
l.add("0");
l.add("1");
l.add("2");
l.add("3");
int size = l.size();
for(int i=0; i < size ; i++){
System.out.println("Removing "+l.get(0));
l.remove(0);
System.out.println("Size is now: "+l.size());
}
for(int i=0;i<l.size();i++){
System.out.println(l.get(i));
}
}
}
//////////////////////////////////////////////////////////////////////////

[Yatendra Varshney]

Hi,

See, your code is running in follwoing manner:
1. Go to first for loop: size of list is 4 and value of i =0.
2. First Attampt: In for loop i < l.size() means 0<4, condition is true go to inside loop and remove "0" from the list and "1" moved to 0th location of the list, now value of list is 3 and i is 1.
Second Attampt: Again go to inside loop and remove "2" because "2" on the 1st position, and then "3" moved to 1th location and then i is 2 and size of list is 2 then condition is false.

[dennis du]

You should use iterator to remove them.

Iterator iterator=list.iterator();
while(iterator.hasNext()){
iterator.remove();
}


So you can scan and remove all of them. It is more reasonable.