title: Adding a JAR into the Android project's /libs folder
body: <p>There are tons of questions about this, but none gives a clear solution to this problem (is it really so difficult?)</p>
  
  <p>I'm trying to add a jar to my Android project. Since r17, Google says we should add the jars to <code>/libs</code> folder, and that the andriod tools will take care of the rest.</p>
  
  <p>I have included a very big library, and it works good, except of one class, so I decided to try and make my own jar.</p>
  
  <p>I created a new java project, and added a simple <code>Test</code> class. Then I exported it as a jar and manually copied the jar into the <code>/libs</code> folder. I cleaned and rebuilt my android app without problems, but at runtime, referencing the Test class, i get the following errors:</p>
  
  <blockquote>
    <p>java.lang.NoClassDefFoundError: mytestpackage.Test</p>
  </blockquote>
  
  <p>When I include the source of the jar into my project directly, it works (of course).</p>
  
  <p>So what am I doing wrong?</p>