title: IntelliJ IDEA: "cannot resolve symbol" for String, System and other Java classes
body: <p>I recently downloaded IntelliJ IDEA to a different computer. On one computer it works fine on the other computer it is giving me this current issue.</p>
  
  <p>When i open a new project with a template it automatically shows errors everywhere even though it allows the code to run and shows the output correctly: standard Java library classes like <code>String</code> and <code>System</code> are highlighted in red and the error tooltip says: "cannot resolve symbol".</p>
  
  <p>I have tried "Invalidate caches/Restart", but it didn't help.</p>
  
  <p><img src="https://i.stack.imgur.com/Kb0fh.png" alt="Basic code showing errors in JDK classes"></p>