title: Eclipse Mars - The project was not built since its build path is incomplete
body: <p>I'm writing an Android application. I want to open it and run it but it is giving 1 error and 1 warning:</p>
  
  <blockquote>
    <p>The project was not built since its build path is incomplete. Cannot
    find the class file for android.content.Context. Fix the build path
    then try building this project The type android.content.Context cannot
    be resolved. It is indirectly referenced from required .class</p>
  </blockquote>
  
  <p>How do I fix this?</p>