 <p>The wiki page says to use a "Java source files", not "Interface Builder Storyboard files" as your screen capture shows. You also need to define an output file, or Xcode ignores the rule (since it doesn't generate anything).</p> <p>I just verified that adding a Java source file to a 6.3.1 project works with the wiki page's instructions. Be sure that your app is selected in the "Add to targets:" when adding the Java source file.</p> <p>Project: <img src="https://i.stack.imgur.com/jt1af.png" alt="enter image description here"></p> <p>Build log: <img src="https://i.stack.imgur.com/KPaiz.png" alt="enter image description here"></p>