code: @Override
      public boolean removeFirstOccurrence(E e) {
          boolean result = queue.removeFirstOccurrence(e);
          if (result) {
              addCapacity(-1);
          }
          return result;
      }
docs: Removes the first occurrence of the specified element in this queue
  when searching it by starting from the head of this queue.
  
  @param e element to be removed.
  @return <code>true</code> if removed successfully, <code>false</code> otherwise