title: Why there is no WeakList and WeakSet implementation in Java?
body: <p>... at least not "official".</p>
  
  <p>You can easily google two or three "WeakList" example implementation and for "WeakSet" one very good can be found in <a href="http://bits.netbeans.org/dev/javadoc/org-openide-util/org/openide/util/WeakSet.html" rel="nofollow noreferrer">NetBeans Platform API</a> sources.</p>
  
  <p>I read <a href="https://stackoverflow.com/questions/4062919/why-does-exist-weakhashmap-but-absent-weakset">similar question</a> placed here asking for WeakSet. Answers were "there is no usecase for WeakSet". If it will be like this why these unofficial implementations exist?</p>