title: Why is package-info.java useful?
body: <p>When I run CheckStyle over my Java project it says <code>Missing package-info.java file.</code> for some classes, but not all of them. I can't really figure out why this message appears only sometimes. Furthermore my project runs perfectly fine without the package-info.java.</p>
  
  <p>What does the package-info.java do? Do I really need it for my Java projects?</p>