jfsm

JVM	Platform	Status
OpenJDK (Temurin) Current	Linux
OpenJDK (Temurin) LTS	Linux
OpenJDK (Temurin) Current	Windows
OpenJDK (Temurin) LTS	Windows

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.