What am I missing? Error message also very confusing

Question about the task

Under discussion

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 a : list)
        {
            if (a.contains("l"))
            {
                list.add(a);
            }

            else if (a.contains("r")||a.contains("l"))
            {
            }

            else if (a.contains("r"))
            {
                list.remove(a);
            }

            else
            {

            }

        }
        return list;
    }
}

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) { list = ArrayList<String>(); for (String a : list) { if (a.contains("l")) { list.add(a); } else if (a.contains("r")||a.contains("l")) { } else if (a.contains("r")) { list.remove(a); } else { } } return list; } }

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Lisa

Level 41

6 August 2021, 08:45

Don't worry, Lisa will rush to your rescue... 🏃‍♀️ So, let's see...🤔 your loop conditions are not logically structured. For example, if you first search for the occurrence of an 'l' and such an 'l' occurs in the string, then the construct is terminated right here and the question of whether an 'l' and 'r' occurs no longer arises (you even didn't check for 'l' and 'r' at all). The following if-else condition is therefore no longer considered at all. You need some new logic here. 💭 Then to the deletion... the nice people from CG have mentioned this but one can't repeat it often enough. You cannot delete from a collection in a for-each loop. Why is that you ask? Once you use an Iterator, you have to use its methods to remove elements from a collection. But why does this cause me problems you ask? Because the for-each loop works internally with an iterator. If you don't use it and change elements of a collection you iterate over, you get a ConcurrentModificationException. And that's no no good for a coder 📉. So instead of using the for-each loop you could declare the Iterator yourself and use its iterate and remove methods, or you could program a normal loop (one using a counter variable) and take care of incrementing the index yourself (sometimes you need to increment, sometimes you need to increment more, and sometimes you don't). Yeah, yeah, I know I am the best 🧐 and I love to bring you wisdom 😜🤪

Lisa

Level 41

6 August 2021, 08:53

Oh, of course I don't want to hide that from you... because I am so ambitious I often program alternative solutions. And coincidentally also for this task (I'm honest, I've written three approaches). The third possibility would be to use a for-each loop over the collection and instead of skipping or deleting elements, copy or not copy them to another list. Now you can't help but love me, yeah, yeah🤪😜 ... dancing in the rain