What is the difference between Strategy design pattern and State design pattern?
What are the differences between the Strategy design pattern and the State design pattern? I was going through quite a few articles on the web but could not make out the difference clearly.
Can someone please explain the difference in layman's terms?
Answer
Honestly, the two patterns are pretty similar in practice, and the defining difference between them tends to vary depending on who you ask. Some popular choices are:
- States store a reference to the context object that contains them. Strategies do not.
- States are allowed to replace themselves (IE: to change the state of the context object to something else), while Strategies are not.
- Strategies are passed to the context object as parameters, while States are created by the context object itself.
- Strategies only handle a single, specific task, while States provide the underlying implementation for everything (or most everything) the context object does.
A "classic" implementation would match either State or Strategy for every item on the list, but you do run across hybrids that have mixes of both. Whether a particular one is more State-y or Strategy-y is ultimately a subjective question.