Java is object oriented so its natural to model a state as an object. Consider (and run) the following program (from here) that models a vending machine; it's a complex program that will take some time to understand; try running it in the debugger:

import java.util.*;
public class StateMachine {
    private enum State {
        // each state and its transitions (actions)
        Ready(true, "Deposit", "Quit"),
        Waiting(true, "Select", "Refund"),
        Dispensing(true, "Remove"),
        Refunding(false, "Refunding"),
        Exiting(false, "Quiting");
        State(boolean is_explicit, String... in) {
            inputs = Arrays.asList(in);
            explicit = is_explicit;
        State nextState(String input, State current) {
            if (inputs.contains(input)) {
                return map.getOrDefault(input, current);
            return current;
        final List<String> inputs;
        final static Map<String, State> map = new HashMap<>();
        final boolean explicit;
        // Map contains transitions, next state
        static {
            map.put("Deposit", State.Waiting);
            map.put("Quit", State.Exiting);
            map.put("Select", State.Dispensing);
            map.put("Refund", State.Refunding);
            map.put("Remove", State.Ready);
            map.put("Refunding", State.Ready);
    public static void main(String[] args) {
        Scanner sc = new Scanner(;
        State state = State.Ready;
        while (state != State.Exiting) {
            if (state.explicit){
                System.out.print("> ");
                state = state.nextState(sc.nextLine().trim(), state);
            } else {
                state = state.nextState(state.inputs.get(0), state);

Read more about implementing state machines in Java in these advanced tutorials here and here

Last modified 19 months ago Last modified on Nov 6, 2019, 2:19:59 PM