What is wrong with my fix method?

Question about the task

R or L

Java Syntax, Level 7, Lesson 9

Under discussion

I don't get why my logic doesn't work

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 s : list){ if (s.contains("r") && s.contains("l")) ; else if (s.contains("r")) list.remove(s); else if (s.contains("l")) list.add(s); } return list; } }

Comments (4)

Popular
New
Old

You must be signed in to leave a comment

Raivo Lapiņš

Level 18 , Riga, Latvia

21 May 2019, 09:22

When I compile your program I get ConcurrentModificationException. This error occurs because here

for(String s : list){
           if (s.contains("r") && s.contains("l"))
               ;
           else if (s.contains("r"))
               list.remove(s);
           else if (s.contains("l"))
               list.add(s);
       }

you are iterating over the list and changing it at the same time. As far as I know Java prohibits such actions in foreach loops. I was able to sort out this problem with regular for(init ; condition ; statement) loop.

Davor Kandic

Level 9 , Beograd, Serbia

21 May 2019, 09:43

Exactly. Or he may use an Iterator object over his list.

Johnson Jose

Level 10 , Edinburgh, United Kingdom

21 May 2019, 10:34

int size= list.size(); String s;
        for(int i = 0; i < size; i++){
            s = list.get(i);
            if (s.contains("r") && s.contains("l"))
                ;
            else if (s.contains("r"))
                list.remove(s);
            else if (s.contains("l"))
                list.add(s);
        }

I've made the following changes, why is there error now?

Raivo Lapiņš

Level 18 , Riga, Latvia

21 May 2019, 10:43

It throws IndexOutOfBoundsException exception. When you remove element from the list your list has one less element, but your iterator i still increases by one and tries to access element that is no longer there.