每次到达char时在下一行打印

Question

In my code I first add two string arrays to a String arrayList. In my toString() method I want to print the arrayList so that every time char ',' is reached, we print the next array, on the next line (in a row). but with this code I get a row of the first array and a column of the second. what am I doing wrong here?

Code :

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class PrintList {
    static String[] data = {"cat","dog"," ","hen",","};
    static String[] data2 = {"ttt","yyy","ggg","ddd", ","};
    static ArrayList <String> list = new ArrayList<>();
    public static void main(String[] args) {
        dataRecord();
        System.out.print(listToString(list));
    }

    public static void dataRecord () {
        list.addAll(Arrays.asList(data));
        list.addAll(Arrays.asList(data2));

    }
    public static String listToString (List <?> list) {
        String result = "";
        for (int i = 0; i < list.size(); i++) {
           result += "      " + list.get(i);
           if (result.indexOf(',') >= 0) {
              result = result + System.lineSeparator();
           }
        }
        return result;
    } 
}

Answer 1

Just change this if:

if (result.indexOf(',') >= 0) 

for this one:

if (list.get(i).indexOf(',') >= 0) 

the problem is that you are always looking in the result variable. When the first ',' appears the result will always contains the ','.

Answer 2

That's some strange code there but I assume it's a learning excercise so it's fine I guess. Your problem is that once your result string contains a comma you add the line separator each time you add a new element.

Example: assume your list contains "a", "b", ",", "c", "d" .

Now you iterate and add the elements to a string which then looks like this:

• you add "a" , the string looks like "a"
• you add "b" , the string looks like "ab"
• you add "," , the string looks like "ab ," , now for the first time your string contains a comma so you add the line separator and thus the string looks like "ab ,\\n"
• you add "c" , the string looks like "ab ,\\nc" . Because there's still a comma in your string another line separtor is added and the string is "ab ,\\nc\\n" .
• you add "d" , the string looks like "ab ,\\nc\\nd" . Because there's still a comma in your string another line separtor is added and the string is "ab ,\\nc\\nd\\n" .

To fix that you have several possibilities:

• check whether the element you just added is a comma or contains one. If so add the line separator (and maybe don't add the element)
• add the elements without any check and replace the commas at the end (after your loop), eg via result = result.replace(",", ",\\n");