Измените регистр символа JavaID

import java.util.Scanner;
public class luck {
    public static  Character hi(Character c,Character d) {
        if (c == 'a' || c == 'b' || c == 'c' || c == 'd' || c == 'e' || c == 'f' || c == 'g' || c == 'q' || c == 'w' || c == 'r' || c == 't' || c == 'y' || c == 'u' || c == 'i' || c == 'o' || c == 'p' || c == 's' || c == 'f' || c == 'g' || c == 'h' || c == 'j' || c == 'k' || c == 'l' || c == 'z' || c == 'x' || c == 'v' || c == 'n' || c == 'm') {
            d = c.toUpperCase(c);
            return d;
        }else  d=c.toLowerCase(c);
        return d;
    }
    
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
         char c=in.next().charAt(0);
        char d=0;
        hi(c,d);
        System.out.println(d);
    }
 
}

import java.util.Scanner;
 
import static java.lang.Character.*;
 
public class luck {
 
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.println("Введите строку ли символ:");
        String line = in.nextLine();
        System.out.println(kalyakaMalyaka(line));
    }
 
    static String kalyakaMalyaka(String line) {
        char[] arr = line.toCharArray();
        for (int i = 0; i < arr.length; i++) {
            if (isLetter(arr[i])) arr[i] = invertCase(arr[i]);
        }
        return String.valueOf(arr);
    }
 
    private static char invertCase(char ch) {
        if (isLowerCase(ch)) ch = toUpperCase(ch);
        else ch = toLowerCase(ch);
        return ch;
    }
}