Java Substring Comparisons

import java.util.Scanner;

public class Solution {

    public static String getSmallestAndLargest(String s, int k) {
        String smallest = "";
        String largest = "";

        String[] list = new String[s.length() - k + 1];
        for (int i = 0; i <= s.length() - k; i++) {
            String str = s.substring(i, i+k);
            list[i] = str;
        }

        smallest = list[0];
        largest = list[0];
        for(int i = 1; i < list.length; i++) {
            if (list[i].compareTo(smallest) < 0) {
                smallest = list[i];
            }

            if (list[i].compareTo(largest) > 0){
                largest = list[i];
            }
        }


        return smallest + "\n" + largest;
    }


    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String s = scan.next();
        int k = scan.nextInt();
        scan.close();
      
        System.out.println(getSmallestAndLargest(s, k));
    }
}