title: How to generate random code for Android application email verification
body: <p>I am writing a new Android application that require the users to register and the system need to send emails to give them a code for email verification.</p>
  
  <p>The random code need to be a 6-digit code that consisting numbers with uppercase alphabet, for example, 6H94BA. I have done some research and still cannot find anything. How to do that?</p>