State Machines

• A system or process, where it can only be in one state at a time

• A collection of states, which when triggered by an event starts a transitions a state from the old state to a new state.

• These events can be

  • Times/dates/timers will do something

  • incoming request to the system (http request, gui trigger)

  • Scheduled action

  • listening for some change somewhere (filesytem being updated, a queue)

• When in the new state, it will take some actions

  • ie store the state in the database, inform the user (request/gui update), validate next transition from event (is event legal)

• https://medium.com/datadriveninvestor/state-machine-design-pattern-why-how-example-through-spring-state-machine-part-1-f13872d68c2d

Examples

• https://github.com/shanwu/finite_state_machine/tree/master/FiniteStateMachine/src/main/java/FiniteStateMachine

• https://www.baeldung.com/java-enum-simple-state-machine

• https://blog.frankel.ch/builder-pattern-finite-state-machine/

• https://medium.com/datadriveninvestor/state-machine-design-pattern-part-2-state-pattern-vs-state-machine-3010dd0fcf28

• https://rclayton.silvrback.com/use-state-machines

• http://www.java2s.com/Code/Java/Collections-Data-Structure/AprogrammableFiniteStateMachineimplementation.htm