Checking if a String contains a letter

Question

I wanted to check if all the Strings from my ArrayList contain a letter "L".

If yes - than the string should have been removed.

I wonder why not every string with "L" was removed?

The result is:

Rose
Leier
Rose
Rose
Rose

Code:

list.add("Leier");
list.add("Rose");
list.add("Liebe");
list.add("Leier");
list.add("Leier");
list.add("Rose");
list.add("Leier");
list.add("Rose");
list.add("Leier");
list.add("Rose");
list.add("Leier");

for (int i = 0; i < list.size(); i++) {
    if (list.get(i).matches(".*[L].*")) {
            list.remove(i);
    }
}

Rather than a regex to check for a single character, why not ``list.get(i).contains("L");`` — NomadMaker, Jul 26 '20 at 17:08

Joni · Accepted Answer · 2020-07-26T16:37:46.630

When you remove an item from a list, it shifts all the remaining items towards the front of the list. So let's say you remove the item at index 5: now the item at index 6 shifts to the position of 5, and 7 to 6, and so on.

After removing the item you increment i, so next you examine index 6. But index 6 contains the item that used to be in index 7 - you've skipped over an item!

There are several ways to fix this. One is using the higher level removeIf method.

    list.removeIf(item -> item.matches(".*[L].*"));

Another is using an Iterator to iterate over the list, and remove items.

    for (Iterator<String> iterator = list.iterator(); iterator.hasNext(); ) {
        String item = iterator.next();
        if (item.matches(".*[L].*")) {
            iterator.remove();
        }
    }

A third is reversing the order of iteration: if you iterate starting from the back of the list, changes to the list indices don't affect you.

    for (int i = list.size() - 1; i >= 0; i--) {
        if (list.get(i).matches(".*[L].*")) {
            list.remove(i);
        }
    }

By the way, if you really only need to check if a string contains the letter L, it's easier to use the contains method instead of matches: item.contains("L")

Thank you Joni for the explanation! It worked with iterator :) — alvira, Jul 26 '20 at 16:37

score -1 · Answer 2 · edited Oct 15 '20 at 11:02

-1

Try this, don't forget to make it lower case

for (int i = 0; i < list.size(); i++) {
            if (list.get(i).toString().toLowerCase().contains("l")) {

                list.remove(i);
            }
        }

edited Oct 15 '20 at 11:02

Marios

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answered Jul 26 '20 at 16:30

Badr Alwattar

42
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There are no lower-case 'L' characters in the input, and even if there were, one should rather use `equalsIgnoreCase();`. – Giorgi Tsiklauri Jul 26 '20 at 16:32
different thinking logic no more than that :) – Badr Alwattar Jul 26 '20 at 17:10

Checking if a String contains a letter

2 Answers2