Design Patterns Field Guide

The Strategy pattern replaces a long chain of if statements with a family of interchangeable objects. A PaymentProcessor holds a reference to a PaymentStrategy and simply calls pay(amount).

Each concrete strategy — card, mobile money, bank transfer — implements the same interface. New strategies can be added without modifying the processor.

Strategy is polymorphism made deliberate: behaviour is selected by choosing an object, not by branching on a flag.