Which kind of exception will be thrown from the following Java program?

public class Test $\{$

public static void main$($String$[]$ args$)\{$

String s $=$ "abcdef"; System.out.println$($s$.$charAt$(6))$;

$\}$

$\}$

a$.$ ArithmeticException b$.$ StringIndexOutOfBoundsException

c$.$ ClassCastException d$.$ No exception