Very efficient Fibonacci algorithm that caches previous values to save on calculation times

Fibonacci.java

package com.supaham.test;

import java.math.BigInteger;
import java.util.HashMap;
import java.util.Map;

public class Fibonacci {

  private static Map<BigInteger, BigInteger> fibIndex = new HashMap<>();
  private static final BigInteger TWO = BigInteger.valueOf(2);

  public static void main(String[] args) {
    long start = System.currentTimeMillis();
    for (int i = 0; i < 1000; i++) {
      System.out.println(i + " " + F(BigInteger.valueOf(i)));
    }
    System.out.println("Done in " + (System.currentTimeMillis() - start) + "ms.");
  }

  public static BigInteger F(BigInteger number) {
    if (number.equals(BigInteger.ZERO)) {
      return BigInteger.ZERO;
    } else if (number.equals(BigInteger.ONE)) {
      return BigInteger.ONE;
    } else {
      if (fibIndex.containsKey(number)) {
        return fibIndex.get(number);
      }
      BigInteger l = F(number.subtract(BigInteger.ONE)).add(F(number.subtract(TWO)));
      fibIndex.put(number, l);
      return l;
    }
  }
}