**ExtendedPrice** – Calculates the price including order-level discount amount (spread over all return line items in the shipment) _and_ any return line item discount amounts.
**DiscountedPrice** – Only calculates the price with the "line item discount amount," that is, the discount for a specific return line item.
**SalesTax** – Calculates sales tax for a return line item.

## Change the default calculation
By inheriting from the default implementation of the interface, DefaultReturnLineItemCalculator, you override the calculations. Just override one or more methods in DefaultReturnLineItemCalculator.
## Change the default validation
The default implementation validates that the return values are not negative after the calculation. To change the behavior, override the validation methods, depending on which validation you should override.