Error with compilation that I don't get

Question about the task

Under discussion

I don't get what intelliJ is telling me : Exception in thread "main" java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:911) at java.util.ArrayList$Itr.next(ArrayList.java:861) at com.codegym.task.task07.task0716.Solution.fix(Solution.java:24) at com.codegym.task.task07.task0716.Solution.main(Solution.java:16) How to fix the problem? And what is the problem in the first case?

1. Create a list of words and populate it yourself.
2. The fix method should:
2.1. remove all words containing the letter "r" from the list
2.2. duplicate all words containing the letter "l".
2.3. if a word contains both "r" and "l", then leave it unchanged.
2.4. don't do anything to other words.

For example:
rose lyre love

Output:
lyre love love

Requirements:

The program must not read data from the keyboard.
The fix method should remove all words containing the letter "r" from the list. There is an exception: words containing both "r" and "l" should be left alone.
The fix method must duplicate words containing the letter "l" (add another instance of this word to the list). There is an exception: words containing both "l" and "r" should not be duplicated.
The fix method should not do anything with words that contain both "l" and "r".
The fix method should not do anything with words that don't contain either "l" or "r".

package com.codegym.task.task07.task0716; import java.util.ArrayList; /* R or L */ public class Solution { public static void main(String[] args) throws Exception { ArrayList<String> list = new ArrayList<String>(); list.add("rose"); // 0 list.add("love"); // 1 list.add("lyre"); // 2 list = fix(list); for (String s : list) { System.out.println(s); } } public static ArrayList<String> fix(ArrayList<String> list) { for(String element : list) { char[] ch = element.toCharArray(); for(int i = 0; i <ch.length; i++){ if(ch[i] == 'r' && ch[i] == 'l') { break; } if(ch[i] == 'r') { list.remove(element); } if(ch[i] == 'l') { list.add(list.indexOf(element), element); } } } return null; } }

Comments (1)

Popular
New
Old

You must be signed in to leave a comment

Guadalupe Gagnon

Level 37 , Tampa, United States

23 December 2021, 15:08

useful

A concurrent modification exception occurs when a collection (such as a List, Set, Map, etc) is looped over using an enhanced for loop (also called a foreach loop) while items are added/removed from that list within the loop. The exception is thrown only in the case that the loop continues to the next cycle after the offending operation occurs, meaning if the loop stops before the next cycle no exception will be thrown. You were probably unaware of this, which is completely normal as you are learning. I made these mistakes too when I was at the same level. Foreach loops are great to access each item in a collection when you don't need to add/remove any of them, say as in just printing all the items. When you need to loop over the items and potentially add/remove any of them then it is 99% likely that a foreach loop will not work. You should use any other loop, even a standard for loop.