Fib.java

import java.util.ArrayList;

class Fib {

  public static int plain(int index) {
    if (index == 0) {
      return 0;
    } else if (index == 1) {
      return 1;
    } else {
      return plain(index - 1) + plain(index - 2);
    }
  }

  public static int cached(int index) {

    ArrayList<Integer> values = new ArrayList<Integer>();
    values.add(0);
    values.add(1);

    for (int i = 0; i <= index; i++) {
      try {
        values.get(i);
      } catch (IndexOutOfBoundsException exception) {
        values.add(values.get(i - 1) + values.get(i - 2));
      }
    }
    return values.get(index);
  }

  public static void main(String[] args) {
    int n = Integer.parseInt(args[0]);
    System.out.println(Fib.plain(n));
    System.out.println(Fib.cached(n));
  }
}

fib.rb

#!/usr/bin/env ruby

class Fib

  def self.plain(index)
    case index
    when 0; 0
    when 1; 1
    else plain(index-1) + plain(index-2)
    end
  end

  def self.cached(index)
    fibs = [0, 1]
    (0..index).each do |i|
      fibs[i] ||= fibs[i-1] + fibs[i-2]
    end
    fibs[index]
  end
end

if __FILE__ == $0
  unless ARGV.length == 1 && ARGV[0] =~ /\d+/
    warn "Syntax: #{$0} N"
    exit false
  end
  puts Fib.cached ARGV[0].to_i
end