Removing every 2nd element in array list

Question

I've been trying so far to write a method ,removeEvenLength that takes an ArrayList of Strings as a parameter and that removes all of the strings of even length from the list. But so far I've been getting a IndexOutOfBoundsException and I don't know why.

Any help would be appreciated

public static ArrayList<String> removeEvenLength(ArrayList<String> list) {
int size = list.size();
ArrayList<String> newLst = new ArrayList<String>();

for (int x = 0; x < size; x++) {
    if (list.get(x).length() % 2 == 0) {
        list.remove(x);
    }
}

return list;

}

You need to use an iterator if you want to remove while iterating. — Tim Biegeleisen, Apr 01 '18 at 06:19
Also, your method return type, and the presence of newLst, shows that you in fact want to create and return a filtered copy of the original list. So you don't even need to remove anything. — JB Nizet, Apr 01 '18 at 06:20
@ElliottFrisch no, that's no what the OP wants to achieve (although the title says so) — JB Nizet, Apr 01 '18 at 06:24
@JBNizet Oops. `return list.stream().filter(s -> s.length() % 2 != 0).collect(Collectors.toList());` — Elliott Frisch, Apr 01 '18 at 06:26

score 1 · Answer 1 · answered Apr 01 '18 at 06:18

Once you remove an element, the size of the list reduces by one and hence the variable size no longer denotes the true size of the list

Also, after you remove a String at index i, the elements from i+1, i+2.. list.size() - 1 will be moved to the left by one position. So, incrementing the loop counter x all the time is wrong and you will skip some elements.

Here's a way to do it right

for (int x = 0; x < list.size();) {
    if (list.get(x).length() % 2 == 0) {
        list.remove(x);
    } else {
        x++;
    }
}

dryleaf · Answer 2 · 2018-04-01T06:33:54.937

0

public static List<String> removeEvenLength(List<String> list) { 
 List<String> newList = new ArrayList<String>();
 for (String item: list) { 
       if (item.length % 2 != 0) {
             newList.add(item); 
        }
  }
 return newList;
}

edited Apr 01 '18 at 06:33

answered Apr 01 '18 at 06:25

dryleaf

415
3
18

You cannot remove an item from the list when using the implicit iterator – Thiyagu Apr 01 '18 at 06:27
For real? Are you going to downvote my answer for no reason? – dryleaf Apr 01 '18 at 06:35
I have already told you the reason I guess – Thiyagu Apr 01 '18 at 06:36
Did you read my answer? – dryleaf Apr 01 '18 at 06:37
See, I downvoted for the [first version](https://stackoverflow.com/revisions/2cfbefc6-b268-4449-9a13-7a176114d6a0/view-source) of your answer. And you didn't mention that you have edited it afterwards – Thiyagu Apr 01 '18 at 06:39

Removing every 2nd element in array list

2 Answers2