java面试题：递归方法

今天参加了一场java笔试，考了斐波那契 数列。以前也见过考阶乘的。今天顺手把它写下来。

public class Recursion {

 public static long factorial(int i) {
  if (i < 0)
   return -1;
  else if (i == 0 || i == 1)
   return 1;
  else
   return i * factorial(i - 1);
 }

 public static int sum(int i) {
  if (i == 0)
   return 0;
  else
   return i + sum(i - 1);
 }

 public static int fibonacci(int i) {
  if (i == 0 || i == 1)
   return 1;
  else
   return fibonacci(i - 1) + fibonacci(i - 2);
 }

 public static void main(String[] args) {
  for (int i = 0; i < 5; i++) {
   System.out.println(i + "!= " + factorial(i));
   System.out.println("sum(" + i + "!) = " + sum(i));
   System.out.println("fibonacci(" + i + ")= " + fibonacci(i));
   System.out.println("=========================");
  }
 }

}