Add subtype inclusion for event handlers

README.md

@@ -51,6 +51,15 @@ public class SimpleEventListener implements EventListener {
 In this case, an event bus is created and used locally.
 In a more sophisticated example the class would acquire an external event bus that is used by multiple classes.
 
+## Event handlers for subtypes
+
+On certain occasions its practical for an event handler to accept both events of the specified type, as well as subclasses of that event.
+To include subtypes for an event handler, use the `includeSubtypes` parameter as follows:
+
+```java
+@Event(includeSubtypes = true)
+```
+
 ## Parameter-less event handlers
 
 In some cases an event handler is not interested in the dispatched event instance.
@@ -82,7 +91,7 @@ To include it inside your project, just add the Maven repository and the depende
     <dependency>
         <groupId>dev.kske</groupId>
         <artifactId>event-bus</artifactId>
-        <version>0.0.3</version>
+        <version>0.0.4</version>
     </dependency>
 </dependencies>
 ```

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>dev.kske</groupId>
 	<artifactId>event-bus</artifactId>
-	<version>0.0.3</version>
+	<version>0.0.4</version>
 
 	<name>Event Bus</name>
 	<description>An event handling framework for Java utilizing annotations.</description>

src/main/java/dev/kske/eventbus/Event.java

@@ -36,6 +36,13 @@ public @interface Event {
 	 */
 	int priority() default 100;
 
+	/**
+	 * Defines whether instances of subtypes of the event type are dispatched to the event handler.
+	 *
+	 * @since 0.0.4
+	 */
+	boolean includeSubtypes() default false;
+
 	/**
 	 * Defines the event type the handler listens to. If this value is set, the handler is not
 	 * allowed to declare parameters.

src/main/java/dev/kske/eventbus/EventBus.java

@@ -31,7 +31,7 @@ public final class EventBus {
 		return singletonInstance;
 	}
 
-	private final Map<Class<? extends IEvent>, Collection<EventHandler>> bindings
+	private final Map<Class<? extends IEvent>, TreeSet<EventHandler>> bindings
 		= new ConcurrentHashMap<>();
 	private final Set<EventListener> registeredListeners = ConcurrentHashMap.newKeySet();
 
@@ -55,8 +55,20 @@ public final class EventBus {
 	 * @since 0.0.1
 	 */
 	private List<EventHandler> getHandlersFor(Class<? extends IEvent> eventClass) {
-		return bindings.containsKey(eventClass) ? new ArrayList<>(bindings.get(eventClass))
-			: new ArrayList<>();
+
+		// Get handlers defined for the event class
+		Set<EventHandler> handlers
+			= bindings.containsKey(eventClass) ? bindings.get(eventClass)
+				: new TreeSet<>();
+
+		// Get subtype handlers
+		for (var binding : bindings.entrySet())
+			if (binding.getKey().isAssignableFrom(eventClass))
+				for (var handler : binding.getValue())
+					if (handler.includeSubtypes())
+						handlers.add(handler);
+
+		return new ArrayList<>(handlers);
 	}
 
 	/**

src/main/java/dev/kske/eventbus/EventHandler.java

@@ -117,6 +117,12 @@ final class EventHandler implements Comparable<EventHandler> {
 	 */
 	int getPriority() { return annotation.priority(); }
 
+	/**
+	 * @return whether this handler includes subtypes
+	 * @since 0.0.4
+	 */
+	boolean includeSubtypes() { return annotation.includeSubtypes(); }
+
 	/**
 	 * @return the event type this handler listens to
 	 * @since 0.0.3

src/test/java/dev/kske/eventbus/EventBusTest.java

@@ -1,6 +1,6 @@
 package dev.kske.eventbus;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.*;
 
 import org.junit.jupiter.api.*;
 
@@ -21,18 +21,29 @@ class EventBusTest implements EventListener {
 
 	@Test
 	void testDispatch() {
+		EventBus.getInstance().dispatch(new SimpleEventSub());
 		EventBus.getInstance().dispatch(new SimpleEvent());
 	}
 
-	@Event(priority = 50)
-	private void onSimpleEventSecond(SimpleEvent event) {
+	@Event(
+		eventType = SimpleEvent.class,
+		includeSubtypes = true,
+		priority = 200
+	)
+	private void onSimpleEventFirst() {
 		++hits;
-		assertEquals(2, hits);
+		assertTrue(hits == 1 || hits == 2);
 	}
 
 	@Event(eventType = SimpleEvent.class, priority = 150)
-	private void onSimpleEventFirst() {
+	private void onSimpleEventSecond() {
 		++hits;
-		assertEquals(1, hits);
+		assertEquals(3, hits);
+	}
+
+	@Event(priority = 50)
+	private void onSimpleEventThird(SimpleEvent event) {
+		++hits;
+		assertEquals(4, hits);
 	}
 }

src/test/java/dev/kske/eventbus/SimpleEventSub.java

@@ -0,0 +1,9 @@
+package dev.kske.eventbus;
+
+/**
+ * Subclass of {@link SimpleEvent} for testing purposes.
+ *
+ * @author Kai S. K. Engelbart
+ * @since 0.0.4
+ */
+public class SimpleEventSub extends SimpleEvent {}