Question

Can somebody explain to me whats wrong with the below piece of code ?

public static void main(String[] args) {
 List<String> l = new ArrayList<String>();
  l.add("1");
  l.add("2");
  l.add("3");
  l.add("4");

  for (int i = 0; i < l.size(); i++) {
   if(l.get(i).equals("1"))
    l.remove(l.get(i));
   else
    System.out.println(l.get(i));
  }
 }

gives me an output of [3.4] instead of [2,3,4] .. Wheres my [2] ? I am a lil confused with this behavior of the List.. Great if somebody could explain..

Thanks in advance 🙂

Answer 1

The reason is:
When i = 0 you remove the first element and i becomes 1
When i = 1 you are now at the third element, because you have shifted everything down by 1 so you write “3”
When i = 2 you write the third element which is “4”

Giving you an output of “3”,”4″

An alternate implementation might be:

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Item {
    public static void main(String[] args) {
        List<String> l = new ArrayList<String>();
        l.add("1");
        l.add("2");
        l.add("3");
        l.add("4");

        Iterator<String> iter = l.iterator();
        while(iter.hasNext())
        {
            String value = iter.next();
            if("1".equals(value))
            {
                iter.remove();
            }
            else
            {
                System.out.println(value);
            }
        }
    }
}