code: private final void clearUnreferencedEntries()
      {
          for (WeakEntry entry = (WeakEntry) queue.poll(); entry != null; entry = (WeakEntry) queue.poll()) {
              WeakEntry removedEntry = (WeakEntry) super.remove(entry.key);
              // The entry for this key may have been replaced with another one after it was dereferenced.
              // Make sure we removed the correct entry.
              if (removedEntry != entry) {
                  super.put(entry.key, removedEntry);
              }
          } // for...
      }
docs: Remove the unreferenced Entries from the map.