title: Can we run service without creating activity ? if yes why ? or if not then why not?
body: <p>1.i just wanted to know can i start the the service without creating activity in android. if yes why ? or if not then why not?</p>
  
  <ol>
  <li>can i put my service creation code in oncreate method directaly?</li>
  <li>Difference between Polymorphism and interface in java?</li>
  </ol>