Java Fib迭代和Fib递归时间比较

Question

Please if you could just check my work and help guide me through the System.currentTimeMillis() function. I understand that it takes a snapshot of my computer time and then when I end it it takes another snap shot and I use the difference of those times to get my run time. Just not sure I'm implementing it properly as my times for my iterative function and my recursive are almost always identical or at most 1 off. I'm confused a little as to if my start time is called again before my iterative starts or if really my time check for iterative time is iterative plus my recursive function. Should I have my total iterative time be endTimeIter - endTimeRecur? Any help is appreciated.

public class FibTest{
    public static void main (String[] args){
        long startTime = System.currentTimeMillis();
        int n = 40;
        System.out.println("The 40th Fibonacci number per my recursive function is: " +    fibRecur(n));
           long endTimeRecur = System.currentTimeMillis();
           long totalTimeRecur = endTimeRecur - startTime;
        System.out.println("The 40th Fibonacci number per my recursive function is: " + fibIter(n));
           long endTimeIter = System.currentTimeMillis();
           long totalTimeIter = endTimeIter - startTime;
        System.out.println("The time it took to find Fib(40) with my recursive method was: " + totalTimeRecur);
        System.out.println("The time it took to find Fib(40) with my iterative method was: " + totalTimeIter);
    }
    public static int fibRecur(int n){
        if (n < 3) return 1;
        return fibRecur(n-2) + fibRecur(n-1);
    }
    public static int fibIter(int n){
        int fib1 = 1;
        int fib2 = 1;
        int i, result = 0;
        for (i = 2; i < n; i++ ){
            result = fib1 + fib2;
            fib1 = fib2;
            fib2 = result;
        }
        return result;
    }  
 }

Answer 1

That's one way of how the time difference must be done

long time = System.currentTimeMillis();
methodA();
System.out.println(System.currentTimeMillis() - time);

time = System.currentTimeMillis();
methodB();
System.out.println(System.currentTimeMillis() - time);

Answer 2

In addition to Amir's answer:

One bug in your program is that you print

System.out.println("The 40th Fibonacci number per my recursive function is: " + fibIter(n));

I think what you want to say is:

System.out.println("The 40th Fibonacci number per my iterative function is: " + fibIter(n));