Strategy Pattern – Shipping Cost Calculator

Overview

This project demonstrates the Strategy Design Pattern using a shipping cost calculator example.
The Strategy Pattern allows selecting an algorithm's behavior at runtime, making it easy to switch between different shipping calculation strategies without modifying the service logic.

---

Project Structure

Classes

• Order
  Represents an order with the following properties:

  • totalWeight (double)
  • destinationZone (String)
  • orderValue (double)

• ShippingStrategy (Interface)
  Declares the method double calculateCost(Order order) that all concrete strategies implement.

• FlatRateShipping
  Calculates shipping as a flat fee regardless of weight, zone, or order value.

• WeightBasedShipping
  Calculates shipping cost based on the total weight of the order.
  Formula: totalWeight × ratePerKG.

• DistanceBasedShipping
  Calculates shipping cost based on the destination zone.

  • ZoneA → multiplier 5
  • ZoneB → multiplier 7
  • Default → multiplier 10
    Formula: ratePerKM × multiplier.

• ThirdPartyAPIShipping
  Simulates a third-party API calculation.
  Formula: baseFee + (orderValue × percentageFee).

• ShippingCostService
  Acts as a context that uses a ShippingStrategy object to calculate shipping.

  • setStrategy() allows switching strategies at runtime.
  • calculateShippingCost(Order order) calculates shipping using the currently set strategy.

• FitnessAppObserverDemo
  Demonstrates creating an order and applying different shipping strategies.

---

How to Run

1. Compile all Java files:

   javac *.java
   

2. Run the FitnessAppObserverDemo class:

   java FitnessAppObserverDemo