Changes between Initial Version and Version 1 of ControlSystems/SoftwareTeam/Training/GettingStarted/StateMachines2

Timestamp:

Nov 6, 2019, 2:19:59 PM (6 years ago)

Author:

David Albert

Comment:

--

ControlSystems/SoftwareTeam/Training/GettingStarted/StateMachines2

@@ +1 @@
+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:
+{{{
+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(System.in);
+        State state = State.Ready;
+ 
+        while (state != State.Exiting) {
+            System.out.println(state.inputs);
+            if (state.explicit){
+                System.out.print("> ");
+                state = state.nextState(sc.nextLine().trim(), state);
+            } else {
+                state = state.nextState(state.inputs.get(0), state);
+            }
+        }
+        sc.close();
+    }
+}
+}}}
+
+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]