jfsm

jfsm

The jfsm package provides implementations of finite state machines.

Features

• Mutable enum-based finite state machines.
• Written in pure Java 17.
• High coverage test suite.
• OSGi-ready.
• JPMS-ready.
• ISC license.

Usage

Declare a type that will be used to represent the states of the FSM. An enum type or a sealed hierarchy is a good choice.

enum TrafficLight
{
  RED,
  YELLOW,
  GREEN
}

Declare the allowed state transitions and build an FSM:

final FSMEnumMutableBuilderType<TrafficLight> b =
  FSMEnumMutable.builder(TrafficLight.RED);
b.addTransition(TrafficLight.RED, TrafficLight.YELLOW);
b.addTransition(TrafficLight.YELLOW, TrafficLight.GREEN);
b.addTransition(TrafficLight.GREEN, TrafficLight.YELLOW);
b.addTransition(TrafficLight.YELLOW, TrafficLight.RED);
var fsm = b.build();

Execute transitions:

assert TrafficLight.RED == m.current();

m.transition(TrafficLight.YELLOW;
assert TrafficLight.YELLOW == m.current();

m.transition(TrafficLight.GREEN;
assert TrafficLight.GREEN == m.current();

m.transition(TrafficLight.YELLOW;
assert TrafficLight.YELLOW == m.current();

m.transition(TrafficLight.RED;
assert TrafficLight.RED == m.current();

m.transition(TrafficLight.YELLOW;
assert TrafficLight.YELLOW == m.current();

m.transition(TrafficLight.GREEN;
assert TrafficLight.GREEN == m.current();

m.transition(TrafficLight.YELLOW;
assert TrafficLight.YELLOW == m.current();

m.transition(TrafficLight.RED;
assert TrafficLight.RED == m.current();

m.transition(TrafficLight.YELLOW;
assert TrafficLight.YELLOW == m.current();

m.transition(TrafficLight.GREEN;
assert TrafficLight.GREEN == m.current();

The FSM will throw an FSMTransitionException if an attempt is made to perform a transition that is not permitted.