Answer:
import java.util.Scanner;
import java.lang.*;
class Main {
public static void main(String[] args) {
boolean exit = false;
Scanner reader = new Scanner(System.in);
while(!exit) {
char c = '?';
while( !Character.isLetter(c)) {
System.out.print("Enter a letter or * to exit: ");
c = reader.next().charAt(0);
if (c == '*') {
exit = true;
break;
}
if (!Character.isLetter(c)) {
System.out.printf("Error: %c is not a letter!\n", c);
}
}
if (Character.isLowerCase(c)) {
System.out.printf("%c in uppercase is %c\n", c, Character.toUpperCase(c));
} else if (Character.isUpperCase(c)) {
System.out.printf("%c in lowercase is %c\n", c, Character.toLowerCase(c));
}
}
reader.close();
}
}
Explanation:
I decided to use the asterisk (*) as exit character.
