Computer Fibonnaci Numbers with BigInteger in java

Problem:

Create a Fibonnaci program in java that calculate the fibbonaci numbers using BigInteger class. Include also iterative and recursive methods for the sake of comparaison.

Output:

Enter a positive int value (q to quit):
40
Iterative Fibonacci: 102334155
Recursion Fibonacci: 102334155
Duration: 2088
Accurate Fibonacci: 102334155
Enter a positive int value (q to quit):
q

Solution:

import java.math.BigInteger;
import java.util.Scanner;

public class FibonacciApp {

 public static void main(String[] args) {
  
  Scanner scan = new Scanner(System.in);
  int n;
  String n_str; 
  long fib_iter, fib_rec, time_in, time_out;
  BigInteger fib_acc;
  
  System.out.println("Enter a positive int value (q to quit):");
  n_str = scan.nextLine();
  
  while(!n_str.equalsIgnoreCase("q")) {
   try {
    n = Integer.parseInt(n_str);
    fib_iter = fibonacci_iter(n);
    System.out.println("Iterative Fibonacci: " + fib_iter);
    
    time_in = System.currentTimeMillis();
    
    fib_rec = fibonacci_rec(n);
    System.out.println("Recursion Fibonacci: " + fib_rec);
    
    time_out = System.currentTimeMillis();
    System.out.println("Duration: " + (time_out-time_in));
    
    fib_acc = fibonacci_acc(n);
    System.out.println("Accurate Fibonacci: " + fib_acc);
    
   } catch (NumberFormatException e) {
    System.out.println("Input must be numeric. Try Again");
   } 
   System.out.println("Enter a positive int value (q to quit):");
   n_str = scan.nextLine();
  }
  
  
 }
 
 private static long fibonacci_iter(int n) {
  
  if (n==0 || n==1) return n;
  else { 
   long previousprev = 0;
   long prev =1; 
   long current = 1L;
   
   for (int i=2 ; i <=n ; i++) {
   current = previousprev + prev; 
   previousprev = prev;
   prev = current;
   
   
   }
  return current;
  }
  
 }
 
 private static long fibonacci_rec(int n) {
  if (n ==0 || n==1 ) 
   return n;
  else 
   return fibonacci_rec(n-1)  + fibonacci_rec(n-2)
; }
 
 private static BigInteger fibonacci_acc(int n) {
  if (n==0 || n==1) 
   return BigInteger.valueOf(n);
  else {
   BigInteger prevprev = BigInteger.ZERO;
   BigInteger prev = BigInteger.ONE;
   BigInteger current = BigInteger.ONE;
   
   for (int i = 2; i <= n ; i++) {
    current = prevprev.add(prev);
    prevprev = prev;
    prev = current;
   }
   return current;
  }
 }
}