Passing HashMap to recursive method doesn't work?

Wonkyung Wayne Kim :

I declare HashMap for memoization and pass it into recursive method but it looks like HashMap doesn't really store data and getting reset each recursive call. Here is an example below:

    public static int fib(int n) {
        Map<Integer, Integer> memo = new HashMap<>();
        return fib(n, memo);
    }

    private static int fib(int n, Map<Integer, Integer> memo) {
        if (n < 0) {
            throw new IllegalArgumentException(
                "Index was negative. No such thing as a negative index in a series.");

        // base cases
        } else if (n == 0 || n == 1) {
            return n;
        }

        // see if we've already calculated this
        if (memo.containsKey(n)) {
            System.out.printf("grabbing memo[%d]\n", n);
            return memo.get(n);
        }

        System.out.printf("computing fib(%d)\n", n);
        int result = fib(n - 1) + fib(n - 2);

        // memoize
        memo.put(n, result);

        return result;
    }

output is like below

computing fib(10)
computing fib(9)
computing fib(8)
computing fib(7)
computing fib(6)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(6)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(7)
computing fib(6)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(8)
computing fib(7)
computing fib(6)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(6)
computing fib(5)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)
computing fib(3)
computing fib(2)
computing fib(4)
computing fib(3)
computing fib(2)
computing fib(2)

But it's working fine if I have HashMap as static variable and declare it out side of my fib() but that's not what I wanted to do. Can anyone help me out?

Thanks.

Jason :

The method fib(int, Map) never actually gets called recursively. The map you create each time is never used. Get rid of fib(int) and replace with calls to fib(int, Map).

fib(n - 1, memo) + fib(n - 2, memo);

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