Past exam of the year 1 of the computer science course of the University of Oxford / 2016 / Imperative programming (resit) / 8 / a / Solution

The Strategy pattern is a behavioral pattern that encapsulates alternative algorithms behind a shared object interface. A context holds a strategy and delegates the relevant operation to it, letting the chosen algorithm vary independently of its caller.

Use it when the same task has interchangeable policies, such as alternative pricing or route-selection algorithms. Supplying a different strategy changes the policy without expanding a chain of type tests in the context, and each policy can be checked independently. Object composition makes the selected strategy replaceable; clients rely on its contract rather than on one concrete implementation.