title: intellij from existing sources wont run
body: <p>I have a couple of class files which i have previously developped with text editor, but want now to use intellij. Ive made a new project from sources. When i click run, i get the error at the bottom, and the run configs open up.</p>
  
  <p>I am working on a simple swing app which i would like to build into a jar when im done.</p>
  
  <p>Insights? i have already poked around to find a solution.</p>
  
  <p><a href="https://i.stack.imgur.com/cRVmp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cRVmp.png" alt="enter image description here"></a> </p>