Java -每n个字符添加一行，而不拆分单词

public class InsertNewLine {
    public static String insertNewLineEveryNCharacters(String input, int n) {
        StringBuilder result = new StringBuilder();
        
        for (int i = 0; i < input.length(); i++) {
            char c = input.charAt(i);
            if (c != ' ' && i % n == 0 && i != 0) {
                result.append(System.lineSeparator());
            }
            result.append(c);
        }
        
        return result.toString();
    }
    
    public static void main(String[] args) {
        String input = "This is a sample string.";
        int n = 5;
        String output = insertNewLineEveryNCharacters(input, n);
        System.out.println(output);
    }
}

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is a 
sample
 strin
g.