title: Runnable interface start method
body: <p>I know that there are two ways to write threads in Java:</p>
  
  <ul>
  <li>Method A: Extend Thread class </li>
  <li>Method B: Use Runnable interface.</li>
  </ul>
  
  <p>When you extend <code>Thread</code> class, and then later on call <code>start()</code> method on that thread, the implementation of <code>start()</code> was defined in <code>Thread</code> class.</p>
  
  <p>But when you implement Runnable interface, you only have definition of <code>start()</code> method and not the body.</p>
  
  <p>So how is is that when you invoke <code>start()</code> method using method B, does Java know what to do?</p>