title: How to create 2 or more classes that interact with each other?
body: <p>How do I create two or more classes that interact with each other? 
  For example, a method in the first class will be <code>static</code>, producing a <em>Fibonacci</em> number for instance, and another method in the second  class will do something with the <em>Fibonacci</em> number which has been created by the method in first class, and how do I extend my classes?</p>