$2.$ Consider the following code for recursive factorial calculation:

$```$

java

public static int factorial$($int n$)\{$

if $($n $==0)$ return $1$;

return n $*$ factorial$($n $-1)$;

$\}$

$```$

a$.$ Please draw a diagram of the function call stack when $\backslash ($ n$=3\backslash ),$ showing the order and return process of each recursive call.