Design Pattern problem involving N states and transitions between them

Question

I have a problem at hand and I am not getting which design pattern to use. The problem goes as such:

I have to build a system which has \'N\' states and my system ha

Answer 1

The first thing I noticed about your example was that State 3 = (State 1 == true && State 2 == true). This will not scale very well as more possible states become involved. If you are only considering whether it is raining or whether it is Sunday, you can have an enumeration like this, with 4 possible types:

enum State { CLEAR_OTHER_DAY, RAINING_OTHER_DAY, CLEAR_SUNDAY, RAINING_SUNDAY }

This would allow you to state conditions cleanly in a switch block when it is time to code. But if you have to also consider whether it is warm outside, you have to add 4 more values to that enum to capture all possible conditions. And later in your project, your code may need to capture more conditions than you currently envision.

As for a design pattern, the State pattern and its Java example on Wikipedia look like a good place to start.

Wikipedia's example has a StateContext class with a method called setState that takes in a name. I thought about suggesting that you add the state determination logic here, but that would make your StateContext class need to get too close to the implementation details of your other classes. It would be better to put a method for determining the system's state in a class that would easily know the conditions for going from one state to another. This way, if your project needs to change in the future and you either have more states to keep track of or different conditions, you only need to maintain the logic in one place.