code: private synchronized void expungeStaleEntries()
      {
          if (size == 0) return;
          Object r;
          while ((r = queue.poll()) != null)
          {
              Entry e = (Entry) r;
              unlink(e);
              int h = e.hash;
              int i = indexFor(h, table.length);
  
              Entry prev = table[i];
              Entry p = prev;
              while (p != null)
              {
                  Entry next = p.next;
                  if (p == e)
                  {
                      if (prev == e)
                          table[i] = next;
                      else
                          prev.next = next;
                      e.next = null;  // Help GC
                      size--;
                      break;
                  }
                  prev = p;
                  p = next;
              }
          }
      }
docs: Expunge stale entries from the table.