code: public long getEstimate(final T item) {
      // If item is tracked:
      // Estimate = itemCount + offset; Otherwise it is 0.
      final long itemCount = hashMap.get(item);
      return (itemCount > 0) ? itemCount + offset : 0;
    }
docs: Gets the estimate of the frequency of the given item.
  Note: The true frequency of a item would be the sum of the counts as a result of the
  two update functions.
  
  @param item the given item
  @return the estimate of the frequency of the given item