String index out of range: 0

import java.util.Scanner;
 
class MyProgram {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        char letter1 = sc.next().charAt(0);
        char letter2 = sc.next().charAt(0);
        String str = sc.nextLine();
        String[] words = str.split(" ");
        for(int i = 0; i < words.length; i++) {
           if(words[i].charAt(0) >= letter1 && words[i].charAt(0) <= letter2) System.out.print(words[i]);
        }
    }
}

        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        char letter1 = str.charAt(0);
        char letter2 = str.charAt(1);
        str = sc.nextLine();
        String[] words = str.split(" ");
        for(int i = 0; i < words.length; i++) {
            if (words[i].length() > 0 && words[i].charAt(0) >= letter1 && words[i].charAt(0) <= letter2)
                System.out.print(words[i] + " ");
        }

        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        Matcher m = Pattern.compile(String.format("\\b[%c-%c]\\w*", str.charAt(0), str.charAt(1))).matcher(sc.nextLine());
        while (m.find()) System.out.print(m.group() + " ");

public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        char letter1 = sc.next().charAt(0);
        char letter2 = sc.next().charAt(0);
        sc.skip("\n");
        String str = sc.nextLine();
        String[] words = str.split(" ");
        for(int i = 0; i < words.length; i++) {
            if(words[i].charAt(0) >= letter1 && words[i].charAt(0) <= letter2) System.out.print(words[i]);
        }
    }

import java.util.Scanner;
 
class MyStudy {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String letter = sc.nextLine().toLowerCase();
        while (sc.hasNext()) {
            String s = sc.next();
            if (s.charAt(0) >= letter.charAt(0) && s.charAt(0) <= letter.charAt(2)) {
                System.out.println(s);
            } 
        }
    }
}