title: What is callable in Java?
body: <p>The title pretty much sums it. </p>
  
  <p>I want to know the concept and idea of callable . I have read a <a href="https://stackoverflow.com/questions/141284/the-difference-between-the-runnable-and-callable-interfaces-in-java">question here</a> on difference between callable and runnable. but no one show code and give detail what a callable is. I don't want to know the difference between them. I want to know ,</p>
  
  <ol>
  <li><p>What is a callable ?</p></li>
  <li><p>When to use them and how to use them . </p></li>
  <li><p>When they come in action for
      Android.</p></li>
  </ol>