Strategy | Cheat Sheet

Behavioral Pattern — Design Patterns Series

Real-life examples

  • Selection of a sorting algorithm (MergeSort, QuickSort, HeapSort, …) at runtime
  • Selection of a browser storage (local storage, session storage, … ) at runtime
  • Building a hamburger
  • Using different kinds of encryption and decryption
  • Using different kinds of data compression
  • Using different golf clubs for different terrains
  • Travelling options from A to B


  • Definition of a family of individually encapsulated and exchangeable algorithms
  • Allows variable and client independent use of an algorithm

Applicability (suitable if …)

  • A way must be provided to equip a class with one of many different behaviors
  • Different variants of an algorithm are necessary (e.g. different trade-offs between memory requirements and computation time)
  • The implementation of different variants of a class hierarchy of algorithms is necessary
  • An algorithm uses data of which the client has/should have no knowledge
  • Conditional statements are supposed to be wrapped in a separate class

Assets and Drawbacks

  • Emergence of a family of related algorithms (or behaviors)
  • An alternative to creating subclasses (composition makes the algorithm easily modifiable, replaceable, and extensible)
  • Eliminates the need for conditional statements due to polymorphism (e.g. when refactoring switch statements)
  • Different choices of implementations of the same behavior (tradeoff between memory requirements and computation time)
  • The client sometimes needs to know how Strategies differ from each other (conditional disclosure of implementations)
  • Additional effort in communication between Strategy and Context
  • Increased number of objects


For this example I choose a simple Strategy to switch between different sort algorithms at run time. In order to be able to use Dependency Inversion, you first need an interface:


Design Patterns are an important resource and base knowledge for every developer — they are very helpful for solving programmatic problems, help with consistent communication with other developers about system design, and serve as a significant introduction into object composition (besides inheritance) and dependency inversion.



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