Memoized Fibonacci calculation using lambdas in Java 8

MemoizedLambdaFib.java

public class MemoizedLambdaFib {
    interface MemoizedFunction<T, R> {
        enum Cache {
            _;

            Map<Object, Object> vals = new HashMap<>();
        }

        R calc(T t);

        public default R apply(T t) {
            if (!Cache._.vals.containsKey(t)) {
                Cache._.vals.put(t, calc(t));
            }
            return (R)Cache._.vals.get(t);
        }
    }

    static final MemoizedFunction<Integer, Integer> fib = (Integer n) -> {
        if (n == 0 || n == 1) return n;
        return fib.apply(n - 1)+fib.apply(n-2);
    };

    public static void main(String[] args) {
        System.out.println(fib.apply(20));
    }
}

Great comment! Thank you for letting me know abou computeIfAbsent. Sorry I didn't see this sooner!