State machine with Jackson serialization

State.java

package manu.sandbox.demos;

import com.fasterxml.jackson.annotation.JsonValue;
import com.google.common.collect.Sets;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * State machine with Jackson serialization
 */
public enum State {
    ON,
    OFF,
    UNKNOWN;

    public static final Map<State, Set<State>> allowedTransitions = new HashMap<State, Set<State>>() {
        {
            put(ON, s(OFF, UNKNOWN));
            put(UNKNOWN, s(ON));
        }
    };

    public static boolean isAllowed(State fromState, State toState) {
        Set<State> allowedStates = allowedTransitions.get(fromState);
        return allowedStates == null || allowedStates.isEmpty() || allowedStates.contains(toState);
    }

    public static Set<State> nextStates(State fromState) {
        return allowedTransitions.get(fromState);
    }

    private static Set<State> s(State... states) {
        return Sets.newHashSet(states);
    }

    @JsonValue
    public int value() {
        return ordinal();
    }
}