definition of String who is outside the do block keep getting an error message

/*  So the age old knock knock joke goes like this:

    Person A:  Knock Knock.
    Person B:  Who's there?
    Person A:  Banana
    Person B:  Banana who?
    ...as long as Person A has answered Banana the above repeats endlessly
    ...assuming the person answers Orange we'd see
    Person B:  Orange who?
    ...and then the punchline.
    Person A:  Orange you glad I didn't say Banana again?
    (It's a really bad joke that makes it sound like "Aren't you glad I didn't say Banana again?")

    Let's just assume the only two words passed in from the console from Person B are either banana or orange.
*/

// ====BEGIN PROMPTING CODE====
String Who;
do {
// Person A asks:
console.printf("Knock Knock.\n");

// Person B asks and Person A's response is stored in the String who:
String who = console.readLine("Who's there?  ");

// Person B responds:
console.printf("%s who?\n", who);
}
while(who.equals("banan"));
// ==== END PROMPTING CODE ====