Fibonacci number calculator (recursive + iterative)

public class Main {

    public static void main(String[] args) {

        for (int i = 0; i < 20; i++) {
            System.out.println(fibR(i));
        }

        System.out.println("=============");

        for (int i = 0; i < 20; i++) {
            System.out.println(fibI(i));
        }

    }

    // Recursive fibonacci calculator
    public static int fibR(int n) {
        if (n < 0) {
            throw new IllegalArgumentException();
        } else if (n == 0) {
            return 0;
        } else if (n == 1) {
            return 1;
        } else {
            return fibR(n - 1) + fibR(n - 2);
        }
    }

    // Iterative fibonacci calculator
    public static int fibI(int n){
        if(n < 0){
            throw new IllegalArgumentException();
        } else if(n == 0){
            return 0;
        } else if(n == 1){
            return 1;
        } else {
            int a = 0;
            int b = 1;
            int c = 0;

            for (int i = 1; i < n; i++) {
                c = a + b;
                a = b;
                b = c;
            }
            return c;
        }
    }

}