Changes between Version 3 and Version 4 of ControlSystems/SoftwareTeam/Training/GettingStarted/StateMachines1


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Timestamp:
Nov 6, 2019, 2:18:55 PM (3 years ago)
Author:
David Albert
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  • ControlSystems/SoftwareTeam/Training/GettingStarted/StateMachines1

    v3 v4  
    5353In computer science, we often draw '''state diagrams''' that represent the states and the transitions between states.  Read about them [https://en.wikipedia.org/wiki/State_diagram here]
    5454
    55 Java is object oriented so its natural to model a state as an object.  Consider (and run) the following program (from [https://rosettacode.org/wiki/Finite_state_machine here]) that models a vending machine; it's a complex program that will take some time to understand; try running it in the debugger:
    56 {{{
    57 import java.util.*;
    58  
    59 public class StateMachine {
    60  
    61     private enum State {
    62         // each state and its transitions (actions)
    63         Ready(true, "Deposit", "Quit"),
    64         Waiting(true, "Select", "Refund"),
    65         Dispensing(true, "Remove"),
    66         Refunding(false, "Refunding"),
    67         Exiting(false, "Quiting");
    68  
    69         State(boolean is_explicit, String... in) {
    70             inputs = Arrays.asList(in);
    71             explicit = is_explicit;
    72         }
    73  
    74         State nextState(String input, State current) {
    75             if (inputs.contains(input)) {
    76                 return map.getOrDefault(input, current);
    77             }
    78             return current;
    79         }
    80  
    81         final List<String> inputs;
    82         final static Map<String, State> map = new HashMap<>();
    83         final boolean explicit;
    84  
    85         // Map contains transitions, next state
    86         static {
    87             map.put("Deposit", State.Waiting);
    88             map.put("Quit", State.Exiting);
    89             map.put("Select", State.Dispensing);
    90             map.put("Refund", State.Refunding);
    91             map.put("Remove", State.Ready);
    92             map.put("Refunding", State.Ready);
    93         }
    94     }
    95  
    96     public static void main(String[] args) {
    97         Scanner sc = new Scanner(System.in);
    98         State state = State.Ready;
    99  
    100         while (state != State.Exiting) {
    101             System.out.println(state.inputs);
    102             if (state.explicit){
    103                 System.out.print("> ");
    104                 state = state.nextState(sc.nextLine().trim(), state);
    105             } else {
    106                 state = state.nextState(state.inputs.get(0), state);
    107             }
    108         }
    109         sc.close();
    110     }
    111 }
    112 }}}
    113 
    114 Read more about implementing state machines in Java in these advanced tutorials [https://www.mirkosertic.de/blog/2013/04/implementing-state-machines-with-java-enums/ here] and [https://www.baeldung.com/java-enum-simple-state-machine here]