title: What causes ClassNotFoundException for an unreferenced class?
body: <p>I've encounted an error trying to implement Apache commons-compress in my Java application:</p>
  
  <blockquote>
    <p>java.lang.ClassNotFoundException: org.apache.commons.compress.archivers.ArchiveEntry"</p>
  </blockquote>
  
  <p>I have the exact same issue described in <a href="http://forums.bukkit.org/threads/noclassdeffounderror-for-class-never-mentioned.71917/" rel="nofollow">this post</a>, except I'm not using Bukkit (whatever that is). The [expletive] OP left an infuriating last post, "Regardless, I found a solution. Case closed!" instead of sharing the solution, so I have no idea what (s)he did to resolve it.</p>
  
  <p>I'm not using ArchiveEntry, but rather, TarArchiveEntry, which I assume imports ArchiveEntry. Even if I import the supposedly missing class, Eclipse warns of an unused import. Curiously, if I remove my TarArchiveEntry import, the warning disappears, but the line containing the reference to TarArchiveEntry errors.</p>
  
  <p>I've never experienced this issue before. It would seem that the TarArchiveEntry class contains an error and fails to import ArchiveEntry, but I can't see a widely used library such as apache commons containing such an elementary error.</p>
  
  <p>Is there anything wrong with my implimentation?</p>