title: No IDEA annotations attached to the JDK 1.8 (C:\...), some issues will not be found
body: <p>In Android Studio 3.1.2 I am suddenly getting the following message in a yellow tape frame at the top of my editor:</p>
  
  <blockquote>
    <p>No IDEA annotations attached to the JDK 1.8 (C:\Program Files\Android\Android Studio\jre), some issues will not be found</p>
  </blockquote>
  
  <p>I also have a warning in Edit Configurations:</p>
  
  <blockquote>
    <p>Default Activity not found</p>
  </blockquote>
  
  <p>How can I solve these issues?</p>