Make fields final where appropriate

src/main/java/org/jeasy/states/api/FiniteStateMachineException.java

@@ -34,17 +34,17 @@ public class FiniteStateMachineException extends Exception {
     /**
      * The transition where the exception occurred.
      */
-    private Transition transition;
+    private final Transition transition;
 
     /**
      * The event triggered when the exception occurred.
      */
-    private Event event;
+    private final Event event;
 
     /**
      * The root cause of the exception.
      */
-    private Throwable cause;
+    private final Throwable cause;
 
     /**
      * Create a new {@link FiniteStateMachineException}.

src/main/java/org/jeasy/states/api/State.java

@@ -31,7 +31,7 @@
  */
 public class State {
 
-    private String name;
+    private final String name;
 
     /**
      * Create a new {@link State}.

src/main/java/org/jeasy/states/core/FiniteStateMachineBuilder.java

@@ -54,9 +54,9 @@ public class FiniteStateMachineBuilder {
         }
     }
 
-    private FiniteStateMachineImpl finiteStateMachine;
-    private FiniteStateMachineDefinitionValidator finiteStateMachineDefinitionValidator;
-    private TransitionDefinitionValidator transitionDefinitionValidator;
+    private final FiniteStateMachineImpl finiteStateMachine;
+    private final FiniteStateMachineDefinitionValidator finiteStateMachineDefinitionValidator;
+    private final TransitionDefinitionValidator transitionDefinitionValidator;
 
     /**
      * Create a new {@link FiniteStateMachineBuilder}.

src/main/java/org/jeasy/states/core/FiniteStateMachineImpl.java

@@ -35,10 +35,10 @@ final class FiniteStateMachineImpl implements FiniteStateMachine {
     private static final Logger LOGGER = Logger.getLogger(FiniteStateMachineImpl.class.getSimpleName());
 
     private State currentState;
-    private State initialState;
-    private Set<State> finalStates;
-    private Set<State> states;
-    private Set<Transition> transitions;
+    private final State initialState;
+    private final Set<State> finalStates;
+    private final Set<State> states;
+    private final Set<Transition> transitions;
     private Event lastEvent;
     private Transition lastTransition;
 

src/main/java/org/jeasy/states/core/TransitionBuilder.java

@@ -42,7 +42,7 @@
  */
 public class TransitionBuilder {
 
-    private TransitionImpl transition;
+    private final TransitionImpl transition;
 
     /**
      * Create a new {@link TransitionBuilder}.