A retail application calculates shipping costs using a ShippingCalculator class. Inside this class, the developer uses a massive series of if-else statements checking if (package instanceof StandardBox) else if (package instanceof FragileCrate) to apply different mathematical formulas. Next month, the company plans to introduce a new RefrigeratedContainer package type. How should the developer refactor this code to satisfy the Open/Closed Principle?

Question

A retail application calculates shipping costs using a  ShippingCalculator  class. Inside this class, the developer uses a massive series of  if-else  statements checking  if (package instanceof StandardBox) else if (package instanceof FragileCrate)  to apply different mathematical formulas. Next month, the company plans to introduce a new  RefrigeratedContainer  package type. How should the developer refactor this code to satisfy the Open/Closed Principle?

Answer

Change the if-else block into a switch statement that evaluates the string name of the package, ensuring faster execution when the new container is added.

Answer

Create a Shippable interface with a calculateCost() method, and have each package type implement its own logic.

Answer

Declare the ShippingCalculator class as final so that junior developers cannot accidentally modify the existing if-else block when the new container arrives.

Answer

Extract the calculation logic into a private method within the ShippingCalculator so the mathematical formulas remain securely hidden via encapsulation.

Answer

Utilise aggressive downcasting to convert the generic package into a specific RefrigeratedContainer reference before applying the mathematical formula.

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