docs: public Set tokens() {
          if (tokenSet == null) {
              tokenSet = new AbstractSetView() {
  
                  public long size() throws ObjectManagerException {
                      return directory.size();
                  } // size().
  
                  public Iterator iterator() throws ObjectManagerException {
  
                      final Iterator storeAreaIterator = directory.entrySet().iterator();
                      return new Iterator() {
  
                          public boolean hasNext() throws ObjectManagerException
                          {
                              return storeAreaIterator.hasNext();
                          } // hasNext().
  
                          public Object next() throws ObjectManagerException
                          {
                              Directory.StoreArea storeArea = (Directory.StoreArea) storeAreaIterator.next();
                              Token token = new Token(AbstractSingleFileObjectStore.this, storeArea.identifier);
                              return like(token);
                          } // next().   
  
                          public boolean hasNext(Transaction transaction)
                                          throws ObjectManagerException
                          {
                              throw new UnsupportedOperationException();
                          } // hasNext().
  
                          public Object next(Transaction transaction)
                                          throws ObjectManagerException
                          {
                              throw new UnsupportedOperationException();
                          } // next().
  
                          public Object remove(Transaction transaction)
                                          throws ObjectManagerException
                          {
                              throw new UnsupportedOperationException();
                          } // remove().
                      }; // new Iterator().
                  } // iterator().  
  
              }; // new AbstractSetView().
          } // if (tokenSet == null). 
          return tokenSet;
      }