Merge pull request 'Support JDK-style Javadoc Tags' (#28) from b/javadoc-tags into develop

Reviewed-on: https://git.kske.dev/kske/event-bus/pulls/28
Reviewed-by: delvh <leon@kske.dev>

README.md

@@ -45,9 +45,6 @@ public class SimpleEventListener {
 }
 ```
 
-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.
-
 Note that creating static event handlers like this
 
 ```java

event-bus-core/pom.xml

@@ -16,7 +16,7 @@
 		<dependency>
 			<groupId>org.junit.jupiter</groupId>
 			<artifactId>junit-jupiter-api</artifactId>
-			<version>5.6.2</version>
+			<version>5.8.1</version>
 			<scope>test</scope>
 		</dependency>
 	</dependencies>
@@ -26,5 +26,14 @@
 		<!-- Disable resource folder -->
 		<resources />
 
+		<!-- Run unit tests -->
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<version>3.0.0-M5</version>
+			</plugin>
+		</plugins>
+
 	</build>
 </project>

event-bus-core/src/main/java/dev/kske/eventbus/core/Event.java

@@ -22,7 +22,7 @@ import java.lang.annotation.*;
 public @interface Event {
 
 	/**
-	 * Defines the event type the handler listens to. If this value is set, the handler is not
+	 * Defines the event type the handler listens for. If this value is set, the handler is not
 	 * allowed to declare parameters.
 	 * <p>
 	 * This is useful when the event handler does not utilize the event instance.

event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java

@@ -5,6 +5,9 @@ import java.lang.System.Logger.Level;
 import java.lang.reflect.InvocationTargetException;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Consumer;
+
+import dev.kske.eventbus.core.handler.*;
 
 /**
  * Event listeners can be registered at an event bus to be notified when an event is dispatched.
@@ -27,7 +30,21 @@ public final class EventBus {
 	 */
 	private static final class DispatchState {
 
-		boolean isDispatching, isCancelled;
+		/**
+		 * Indicates that the last event handler invoked has called {@link EventBus#cancel}. In that
+		 * case, the event is not dispatched further.
+		 *
+		 * @since 0.1.0
+		 */
+		boolean isCancelled;
+
+		/**
+		 * Is incremented when {@link EventBus#dispatch(Object)} is invoked and decremented when it
+		 * finishes. This allows keeping track of nested dispatches.
+		 *
+		 * @since 1.2.0
+		 */
+		int nestingCount;
 	}
 
 	/**
@@ -38,33 +55,55 @@ public final class EventBus {
 	 */
 	public static final int DEFAULT_PRIORITY = 100;
 
-	private static volatile EventBus singletonInstance;
+	private static final EventBus singletonInstance = new EventBus();
 
 	private static final Logger logger = System.getLogger(EventBus.class.getName());
 
 	/**
-	 * Produces a singleton instance of the event bus. It is lazily initialized on the first call.
+	 * Compares event handlers based on priority, but uses hash codes for equal priorities.
 	 *
-	 * @return a singleton instance of the event bus.
+	 * @implNote As the priority comparator by itself is not consistent with equals (two handlers
+	 *           with the same priority are not necessarily equal, but would have a comparison
+	 *           result of 0), the hash code is used for the fallback comparison. This way,
+	 *           consistency with equals is restored.
+	 * @since 1.2.0
+	 */
+	private static final Comparator<EventHandler> byPriority =
+		Comparator.comparingInt(EventHandler::getPriority).reversed()
+			.thenComparingInt(EventHandler::hashCode);
+
+	/**
+	 * Returns the default event bus, which is a statically initialized singleton instance.
+	 *
+	 * @return the default event bus
 	 * @since 0.0.2
 	 */
 	public static EventBus getInstance() {
-		EventBus instance = singletonInstance;
-		if (instance == null)
-			synchronized (EventBus.class) {
-				if ((instance = singletonInstance) == null) {
-					logger.log(Level.DEBUG, "Initializing singleton event bus instance");
-					instance = singletonInstance = new EventBus();
-				}
-			}
-		return instance;
+		return singletonInstance;
 	}
 
-	private final Map<Class<?>, TreeSet<EventHandler>>	bindings			=
-		new ConcurrentHashMap<>();
-	private final Set<Object>							registeredListeners	=
-		ConcurrentHashMap.newKeySet();
-	private final ThreadLocal<DispatchState>			dispatchState		=
+	/**
+	 * Event handler bindings (target class to handlers registered for that class), does not contain
+	 * other (polymorphic) handlers.
+	 *
+	 * @since 0.0.1
+	 */
+	private final Map<Class<?>, TreeSet<EventHandler>> bindings = new ConcurrentHashMap<>();
+
+	/**
+	 * Stores all registered event listeners (which declare event handlers) and prevents them from
+	 * being garbage collected.
+	 *
+	 * @since 0.0.1
+	 */
+	private final Set<Object> registeredListeners = ConcurrentHashMap.newKeySet();
+
+	/**
+	 * The current event dispatching state, local to each thread.
+	 *
+	 * @since 0.1.0
+	 */
+	private final ThreadLocal<DispatchState> dispatchState =
 		ThreadLocal.withInitial(DispatchState::new);
 
 	/**
@@ -72,18 +111,21 @@ public final class EventBus {
 	 * priority.
 	 *
 	 * @param event the event to dispatch
-	 * @throws EventBusException if an event handler isn't accessible or has an invalid signature
+	 * @throws EventBusException    if an event handler isn't accessible or has an invalid signature
+	 * @throws NullPointerException if the specified event is {@code null}
 	 * @since 0.0.1
 	 */
 	public void dispatch(Object event) throws EventBusException {
 		Objects.requireNonNull(event);
 		logger.log(Level.INFO, "Dispatching event {0}", event);
 
-		// Set dispatch state
+		// Look up dispatch state
 		var state = dispatchState.get();
-		state.isDispatching = true;
 
-		Iterator<EventHandler> handlers = getHandlersFor(event.getClass());
+		// Increment nesting count (becomes > 1 during nested dispatches)
+		++state.nestingCount;
+
+		Iterator<EventHandler> handlers = getHandlersFor(event.getClass()).iterator();
 		if (handlers.hasNext()) {
 			while (handlers.hasNext())
 				if (state.isCancelled) {
@@ -94,14 +136,14 @@ public final class EventBus {
 					try {
 						handlers.next().execute(event);
 					} catch (InvocationTargetException e) {
-						if (event instanceof DeadEvent || event instanceof ExceptionEvent)
-
-							// Warn about system event not being handled
-							logger.log(Level.WARNING, event + " not handled due to exception", e);
-						else if (e.getCause() instanceof Error)
+						if (e.getCause() instanceof Error)
 
 							// Transparently pass error to the caller
 							throw (Error) e.getCause();
+						else if (event instanceof DeadEvent || event instanceof ExceptionEvent)
+
+							// Warn about system event not being handled
+							logger.log(Level.WARNING, event + " not handled due to exception", e);
 						else
 
 							// Dispatch exception event
@@ -118,8 +160,8 @@ public final class EventBus {
 			dispatch(new DeadEvent(this, event));
 		}
 
-		// Reset dispatch state
-		state.isDispatching = false;
+		// Decrement nesting count (becomes 0 when all dispatches on the thread are finished)
+		--state.nestingCount;
 
 		logger.log(Level.DEBUG, "Finished dispatching event {0}", event);
 	}
@@ -128,23 +170,24 @@ public final class EventBus {
 	 * Searches for the event handlers bound to an event class. This includes polymorphic handlers
 	 * that are bound to a supertype of the event class.
 	 *
-	 * @param eventClass the event class to use for the search
-	 * @return an iterator over the applicable handlers in descending order of priority
-	 * @since 0.0.1
+	 * @param eventType the event type to use for the search
+	 * @return a navigable set containing the applicable handlers in descending order of priority
+	 * @since 1.2.0
 	 */
-	private Iterator<EventHandler> getHandlersFor(Class<?> eventClass) {
+	private NavigableSet<EventHandler> getHandlersFor(Class<?> eventType) {
 
 		// Get handlers defined for the event class
-		TreeSet<EventHandler> handlers = bindings.getOrDefault(eventClass, new TreeSet<>());
+		TreeSet<EventHandler> handlers =
+			bindings.getOrDefault(eventType, new TreeSet<>(byPriority));
 
 		// Get polymorphic handlers
 		for (var binding : bindings.entrySet())
-			if (binding.getKey().isAssignableFrom(eventClass))
+			if (binding.getKey().isAssignableFrom(eventType))
 				for (var handler : binding.getValue())
 					if (handler.isPolymorphic())
 						handlers.add(handler);
 
-		return handlers.iterator();
+		return handlers;
 	}
 
 	/**
@@ -155,7 +198,7 @@ public final class EventBus {
 	 */
 	public void cancel() {
 		var state = dispatchState.get();
-		if (state.isDispatching && !state.isCancelled)
+		if (state.nestingCount > 0 && !state.isCancelled)
 			state.isCancelled = true;
 		else
 			throw new EventBusException("Calling thread not an active dispatching thread!");
@@ -165,8 +208,9 @@ public final class EventBus {
 	 * Registers an event listener at this event bus.
 	 *
 	 * @param listener the listener to register
-	 * @throws EventBusException if the listener is already registered or a declared event handler
-	 *                           does not comply with the specification
+	 * @throws EventBusException    if the listener is already registered or a declared event
+	 *                              handler does not comply with the specification
+	 * @throws NullPointerException if the specified listener is {@code null}
 	 * @since 0.0.1
 	 * @see Event
 	 */
@@ -196,11 +240,8 @@ public final class EventBus {
 				continue;
 
 			// Initialize and bind the handler
-			var handler = new EventHandler(listener, method, annotation, polymorphic, priority);
-			bindings.putIfAbsent(handler.getEventType(), new TreeSet<>());
-			logger.log(Level.DEBUG, "Binding event handler {0}", handler);
-			bindings.get(handler.getEventType())
-				.add(handler);
+			bindHandler(
+				new ReflectiveEventHandler(listener, method, annotation, polymorphic, priority));
 			handlerBound = true;
 		}
 
@@ -211,6 +252,86 @@ public final class EventBus {
 				listener.getClass().getName());
 	}
 
+	/**
+	 * Registers a callback listener, which is a consumer that is invoked when an event occurs. The
+	 * listener is not polymorphic and has the {@link #DEFAULT_PRIORITY}.
+	 *
+	 * @param <E>           the event type the listener listens for
+	 * @param eventType     the event type the listener listens for
+	 * @param eventListener the callback that is invoked when an event occurs
+	 * @since 1.2.0
+	 * @see #registerListener(Class, Consumer, boolean, int)
+	 */
+	public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener) {
+		registerListener(eventType, eventListener, false, DEFAULT_PRIORITY);
+	}
+
+	/**
+	 * Registers a callback listener, which is a consumer that is invoked when an event occurs. The
+	 * listener has the {@link #DEFAULT_PRIORITY}.
+	 *
+	 * @param <E>           the event type the listener listens for
+	 * @param eventType     the event type the listener listens for
+	 * @param eventListener the callback that is invoked when an event occurs
+	 * @param polymorphic   whether the listener is also invoked for subtypes of the event type
+	 * @since 1.2.0
+	 * @see #registerListener(Class, Consumer, boolean, int)
+	 */
+	public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener,
+		boolean polymorphic) {
+		registerListener(eventType, eventListener, polymorphic, DEFAULT_PRIORITY);
+	}
+
+	/**
+	 * Registers a callback listener, which is a consumer that is invoked when an event occurs. The
+	 * listener is not polymorphic.
+	 *
+	 * @param <E>           the event type the listener listens for
+	 * @param eventType     the event type the listener listens for
+	 * @param eventListener the callback that is invoked when an event occurs
+	 * @param priority      the priority to assign to the listener
+	 * @since 1.2.0
+	 * @see #registerListener(Class, Consumer, boolean, int)
+	 */
+	public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener, int priority) {
+		registerListener(eventType, eventListener, false, priority);
+	}
+
+	/**
+	 * Registers a callback listener, which is a consumer that is invoked when an event occurs.
+	 *
+	 * @param <E>           the event type the listener listens for
+	 * @param eventType     the event type the listener listens for
+	 * @param eventListener the callback that is invoked when an event occurs
+	 * @param polymorphic   whether the listener is also invoked for subtypes of the event type
+	 * @param priority      the priority to assign to the listener
+	 * @since 1.2.0
+	 */
+	public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener,
+		boolean polymorphic,
+		int priority) {
+		Objects.requireNonNull(eventListener);
+		if (registeredListeners.contains(eventListener))
+			throw new EventBusException(eventListener + " already registered!");
+		logger.log(Level.INFO, "Registering callback event listener {0}",
+			eventListener.getClass().getName());
+
+		registeredListeners.add(eventListener);
+		bindHandler(new CallbackEventHandler(eventType, eventListener, polymorphic, priority));
+	}
+
+	/**
+	 * Inserts a new handler into the {@link #bindings} map.
+	 *
+	 * @param handler the handler to bind
+	 * @since 1.2.0
+	 */
+	private void bindHandler(EventHandler handler) {
+		bindings.putIfAbsent(handler.getEventType(), new TreeSet<>(byPriority));
+		logger.log(Level.DEBUG, "Binding event handler {0}", handler);
+		bindings.get(handler.getEventType()).add(handler);
+	}
+
 	/**
 	 * Removes a specific listener from this event bus.
 	 *
@@ -221,6 +342,7 @@ public final class EventBus {
 		Objects.requireNonNull(listener);
 		logger.log(Level.INFO, "Removing event listener {0}", listener.getClass().getName());
 
+		// Remove bindings from binding map
 		for (var binding : bindings.values()) {
 			var it = binding.iterator();
 			while (it.hasNext()) {
@@ -231,6 +353,8 @@ public final class EventBus {
 				}
 			}
 		}
+
+		// Remove the listener itself
 		registeredListeners.remove(listener);
 	}
 
@@ -245,6 +369,39 @@ public final class EventBus {
 		registeredListeners.clear();
 	}
 
+	/**
+	 * Generates a string describing the event handlers that would be executed for a specific event
+	 * type, in order and without actually executing them.
+	 *
+	 * @apiNote Using this method is only recommended for debugging purposes, as the output depends
+	 *          on implementation internals which may be subject to change.
+	 * @implNote Nested dispatches are not accounted for, as this would require actually executing
+	 *           the handlers.
+	 * @param eventType the event type to generate the execution order for
+	 * @return a human-readable event handler list suitable for debugging purposes
+	 * @since 1.2.0
+	 */
+	public String printExecutionOrder(Class<?> eventType) {
+		var	handlers	= getHandlersFor(eventType);
+		var	sj			= new StringJoiner("\n");
+
+		// Output header line
+		sj.add(String.format("Event handler execution order for %s (%d handler(s)):", eventType,
+			handlers.size()));
+		sj.add(
+			"==========================================================================================");
+
+		// Individual handlers
+		for (var handler : handlers)
+			sj.add(handler.toString());
+
+		// Bottom line
+		sj.add(
+			"==========================================================================================");
+
+		return sj.toString();
+	}
+
 	/**
 	 * Provides an unmodifiable view of the event listeners registered at this event bus.
 	 *

event-bus-core/src/main/java/dev/kske/eventbus/core/EventBusException.java

@@ -1,14 +1,18 @@
 package dev.kske.eventbus.core;
 
 /**
- * This runtime exception is thrown when an event bus error occurs. This can
- * either occur while registering event listeners with invalid handlers, or when
- * an event handler throws an exception.
+ * This unchecked exception is specific to the event bus and can be thrown under the following
+ * circumstances:
+ * <ul>
+ * <li>An event handler throws an exception (which is stored as the cause)</li>
+ * <li>An event listener with an invalid event handler is registered</li>
+ * <li>{@link EventBus#cancel()} is invoked from outside an active dispatch thread</li>
+ * </ul>
  *
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-public class EventBusException extends RuntimeException {
+public final class EventBusException extends RuntimeException {
 
 	private static final long serialVersionUID = 1L;
 

event-bus-core/src/main/java/dev/kske/eventbus/core/handler/CallbackEventHandler.java

@@ -0,0 +1,73 @@
+package dev.kske.eventbus.core.handler;
+
+import java.lang.reflect.InvocationTargetException;
+import java.util.function.Consumer;
+
+/**
+ * An event handler wrapping a callback method.
+ *
+ * @author Kai S. K. Engelbart
+ * @since 1.2.0
+ */
+public final class CallbackEventHandler implements EventHandler {
+
+	private final Class<?>			eventType;
+	private final Consumer<Object>	callback;
+	private final boolean			polymorphic;
+	private final int				priority;
+
+	/**
+	 * Constructs a callback event handler.
+	 *
+	 * @param <E>         the event type of the handler
+	 * @param eventType   the event type of the handler
+	 * @param callback    the callback method to execute when the handler is invoked
+	 * @param polymorphic whether the handler is polymorphic
+	 * @param priority    the priority of the handler
+	 * @since 1.2.0
+	 */
+	@SuppressWarnings("unchecked")
+	public <E> CallbackEventHandler(Class<E> eventType, Consumer<E> callback, boolean polymorphic,
+		int priority) {
+		this.eventType		= eventType;
+		this.callback		= (Consumer<Object>) callback;
+		this.polymorphic	= polymorphic;
+		this.priority		= priority;
+	}
+
+	@Override
+	public void execute(Object event) throws InvocationTargetException {
+		try {
+			callback.accept(event);
+		} catch (RuntimeException e) {
+			throw new InvocationTargetException(e, "Callback event handler failed!");
+		}
+	}
+
+	@Override
+	public String toString() {
+		return String.format(
+			"CallbackEventHandler[eventType=%s, polymorphic=%b, priority=%d]",
+			eventType, polymorphic, priority);
+	}
+
+	@Override
+	public Consumer<?> getListener() {
+		return callback;
+	}
+
+	@Override
+	public Class<?> getEventType() {
+		return eventType;
+	}
+
+	@Override
+	public int getPriority() {
+		return priority;
+	}
+
+	@Override
+	public boolean isPolymorphic() {
+		return polymorphic;
+	}
+}

event-bus-core/src/main/java/dev/kske/eventbus/core/handler/EventHandler.java

@@ -0,0 +1,53 @@
+package dev.kske.eventbus.core.handler;
+
+import java.lang.reflect.InvocationTargetException;
+
+import dev.kske.eventbus.core.*;
+
+/**
+ * Internal representation of an event handling method.
+ *
+ * @author Kai S. K. Engelbart
+ * @since 1.2.0
+ * @see EventBus
+ */
+public interface EventHandler {
+
+	/**
+	 * Executes the event handler.
+	 *
+	 * @param event the event used as the method parameter
+	 * @throws EventBusException         if the event handler isn't accessible or has an invalid
+	 *                                   signature
+	 * @throws InvocationTargetException if the handler throws an exception
+	 * @throws EventBusException         if the handler has the wrong signature or is inaccessible
+	 * @since 1.2.0
+	 */
+	void execute(Object event) throws EventBusException, InvocationTargetException;
+
+	/**
+	 * @return the listener containing this handler
+	 * @since 1.2.0
+	 */
+	Object getListener();
+
+	/**
+	 * @return the event type this handler listens for
+	 * @since 1.2.0
+	 */
+	Class<?> getEventType();
+
+	/**
+	 * @return the priority of this handler
+	 * @since 1.2.0
+	 * @see Priority
+	 */
+	int getPriority();
+
+	/**
+	 * @return whether this handler also accepts subtypes of the event type
+	 * @since 1.2.0
+	 * @see Polymorphic
+	 */
+	boolean isPolymorphic();
+}

event-bus-core/src/main/java/dev/kske/eventbus/core/handler/ReflectiveEventHandler.java

@@ -1,17 +1,18 @@
-package dev.kske.eventbus.core;
+package dev.kske.eventbus.core.handler;
 
 import java.lang.reflect.*;
 
+import dev.kske.eventbus.core.*;
 import dev.kske.eventbus.core.Event.USE_PARAMETER;
 
 /**
- * Internal representation of an event handling method.
+ * An event handler wrapping a method annotated with {@link Event} and executing it using
+ * reflection.
  *
  * @author Kai S. K. Engelbart
- * @since 0.0.1
- * @see EventBus
+ * @since 1.2.0
  */
-final class EventHandler implements Comparable<EventHandler> {
+public final class ReflectiveEventHandler implements EventHandler {
 
 	private final Object	listener;
 	private final Method	method;
@@ -21,7 +22,7 @@ final class EventHandler implements Comparable<EventHandler> {
 	private final int		priority;
 
 	/**
-	 * Constructs an event handler.
+	 * Constructs a reflective event handler.
 	 *
 	 * @param listener        the listener containing the handler
 	 * @param method          the handler method
@@ -30,10 +31,10 @@ final class EventHandler implements Comparable<EventHandler> {
 	 * @param defPriority     the predefined priority (default or listener-level)
 	 * @throws EventBusException if the method or the annotation do not comply with the
 	 *                           specification
-	 * @since 0.0.1
+	 * @since 1.2.0
 	 */
-	EventHandler(Object listener, Method method, Event annotation, boolean defPolymorphism,
-		int defPriority) throws EventBusException {
+	public ReflectiveEventHandler(Object listener, Method method, Event annotation,
+		boolean defPolymorphism, int defPriority) throws EventBusException {
 		this.listener	= listener;
 		this.method		= method;
 		useParameter	= annotation.value() == USE_PARAMETER.class;
@@ -61,45 +62,13 @@ final class EventHandler implements Comparable<EventHandler> {
 		method.setAccessible(true);
 	}
 
-	/**
-	 * Compares this to another event handler based on priority. In case of equal priority a
-	 * non-zero value based on hash codes is returned.
-	 * <p>
-	 * This is used to retrieve event handlers in descending order of priority from a tree set.
-	 *
-	 * @since 0.0.1
-	 */
 	@Override
-	public int compareTo(EventHandler other) {
-		int priority = other.priority - this.priority;
-		if (priority == 0)
-			priority = listener.hashCode() - other.listener.hashCode();
-		return priority == 0 ? hashCode() - other.hashCode() : priority;
-	}
-
-	@Override
-	public String toString() {
-		return String.format(
-			"EventHandler[method=%s, eventType=%s, useParameter=%b, polymorphic=%b, priority=%d]",
-			method, eventType, useParameter, polymorphic, priority);
-	}
-
-	/**
-	 * Executes the event handler.
-	 *
-	 * @param event the event used as the method parameter
-	 * @throws EventBusException         if the event handler isn't accessible or has an invalid
-	 *                                   signature
-	 * @throws InvocationTargetException if the handler throws an exception
-	 * @throws EventBusException         if the handler has the wrong signature or is inaccessible
-	 * @since 0.0.1
-	 */
-	void execute(Object event) throws EventBusException, InvocationTargetException {
+	public void execute(Object event) throws EventBusException, InvocationTargetException {
 		try {
 			if (useParameter)
-				method.invoke(listener, event);
+				method.invoke(getListener(), event);
 			else
-				method.invoke(listener);
+				method.invoke(getListener());
 		} catch (IllegalArgumentException e) {
 			throw new EventBusException("Event handler rejected target / argument!", e);
 		} catch (IllegalAccessException e) {
@@ -107,29 +76,30 @@ final class EventHandler implements Comparable<EventHandler> {
 		}
 	}
 
-	/**
-	 * @return the listener containing this handler
-	 * @since 0.0.1
-	 */
-	Object getListener() { return listener; }
+	@Override
+	public String toString() {
+		return String.format(
+			"ReflectiveEventHandler[eventType=%s, polymorphic=%b, priority=%d, method=%s, useParameter=%b]",
+			eventType, polymorphic, priority, method, useParameter);
+	}
 
-	/**
-	 * @return the event type this handler listens for
-	 * @since 0.0.3
-	 */
-	Class<?> getEventType() { return eventType; }
+	@Override
+	public Object getListener() {
+		return listener;
+	}
 
-	/**
-	 * @return the priority of this handler
-	 * @since 0.0.1
-	 * @see Priority
-	 */
-	int getPriority() { return priority; }
+	@Override
+	public Class<?> getEventType() {
+		return eventType;
+	}
 
-	/**
-	 * @return whether this handler is polymorphic
-	 * @since 1.0.0
-	 * @see Polymorphic
-	 */
-	boolean isPolymorphic() { return polymorphic; }
+	@Override
+	public int getPriority() {
+		return priority;
+	}
+
+	@Override
+	public boolean isPolymorphic() {
+		return polymorphic;
+	}
 }

event-bus-core/src/main/java/dev/kske/eventbus/core/handler/package-info.java

@@ -0,0 +1,8 @@
+/**
+ * Contains the internal representation of event handling methods.
+ *
+ * @author Kai S. K. Engelbart
+ * @since 1.2.0
+ * @see dev.kske.eventbus.core.handler.EventHandler
+ */
+package dev.kske.eventbus.core.handler;

event-bus-core/src/test/java/dev/kske/eventbus/core/CancelTest.java

@@ -11,7 +11,7 @@ import org.junit.jupiter.api.*;
  * @author Leon Hofmeister
  * @since 0.1.0
  */
-class CancelTest {
+public class CancelTest {
 
 	EventBus	bus;
 	int			hits;
@@ -22,7 +22,7 @@ class CancelTest {
 	 * @since 0.1.0
 	 */
 	@BeforeEach
-	void registerListener() {
+	public void registerListener() {
 		bus = new EventBus();
 		bus.registerListener(this);
 	}
@@ -34,7 +34,7 @@ class CancelTest {
 	 * @since 0.1.0
 	 */
 	@Test
-	void testCancellation() {
+	public void testCancellation() {
 		bus.dispatch(new SimpleEvent());
 		assertEquals(1, hits);
 	}

event-bus-core/src/test/java/dev/kske/eventbus/core/DeadTest.java

@@ -10,7 +10,7 @@ import org.junit.jupiter.api.Test;
  * @author Kai S. K. Engelbart
  * @since 1.1.0
  */
-class DeadTest {
+public class DeadTest {
 
 	EventBus	bus		= new EventBus();
 	String		event	= "This event has no handler";
@@ -18,11 +18,11 @@ class DeadTest {
 
 	/**
 	 * Tests dead event delivery.
-	 * 
+	 *
 	 * @since 1.1.0
 	 */
 	@Test
-	void testDeadEvent() {
+	public void testDeadEvent() {
 		bus.registerListener(this);
 		bus.dispatch(event);
 		assertTrue(deadEventHandled);
@@ -32,11 +32,11 @@ class DeadTest {
 	/**
 	 * Tests how the event bus reacts to an unhandled dead event. This should not lead to an
 	 * exception or an endless recursion and should be logged instead.
-	 * 
+	 *
 	 * @since 1.1.0
 	 */
 	@Test
-	void testUnhandledDeadEvent() {
+	public void testUnhandledDeadEvent() {
 		bus.dispatch(event);
 	}
 

event-bus-core/src/test/java/dev/kske/eventbus/core/DispatchTest.java

@@ -12,7 +12,7 @@ import org.junit.jupiter.api.*;
  */
 @Polymorphic
 @Priority(150)
-class DispatchTest {
+public class DispatchTest {
 
 	EventBus	bus;
 	static int	hits;
@@ -23,9 +23,13 @@ class DispatchTest {
 	 * @since 0.0.1
 	 */
 	@BeforeEach
-	void registerListener() {
+	public void registerListener() {
 		bus = new EventBus();
 		bus.registerListener(this);
+		bus.registerListener(SimpleEvent.class, e -> {
+			++hits;
+			assertEquals(4, hits);
+		});
 	}
 
 	/**
@@ -35,11 +39,30 @@ class DispatchTest {
 	 * @since 0.0.1
 	 */
 	@Test
-	void testDispatch() {
+	public void testDispatch() {
 		bus.dispatch(new SimpleEventSub());
 		bus.dispatch(new SimpleEvent());
 	}
 
+	/**
+	 * Tests {@link EventBus#printExecutionOrder(Class)} based on the currently registered handlers.
+	 *
+	 * @since 1.2.0
+	 */
+	@Test
+	public void testPrintExecutionOrder() {
+		String executionOrder = bus.printExecutionOrder(SimpleEvent.class);
+		System.out.println(executionOrder);
+		assertEquals(
+			"Event handler execution order for class dev.kske.eventbus.core.SimpleEvent (3 handler(s)):\n"
+				+ "==========================================================================================\n"
+				+ "ReflectiveEventHandler[eventType=class dev.kske.eventbus.core.SimpleEvent, polymorphic=true, priority=200, method=void dev.kske.eventbus.core.DispatchTest.onSimpleEventFirst(), useParameter=false]\n"
+				+ "ReflectiveEventHandler[eventType=class dev.kske.eventbus.core.SimpleEvent, polymorphic=false, priority=150, method=static void dev.kske.eventbus.core.DispatchTest.onSimpleEventSecond(), useParameter=false]\n"
+				+ "CallbackEventHandler[eventType=class dev.kske.eventbus.core.SimpleEvent, polymorphic=false, priority=100]\n"
+				+ "==========================================================================================",
+			executionOrder);
+	}
+
 	@Event(SimpleEvent.class)
 	@Priority(200)
 	void onSimpleEventFirst() {
@@ -53,12 +76,4 @@ class DispatchTest {
 		++hits;
 		assertEquals(3, hits);
 	}
-
-	@Event
-	@Polymorphic(false)
-	@Priority(100)
-	void onSimpleEventThird(SimpleEvent event) {
-		++hits;
-		assertEquals(4, hits);
-	}
 }

event-bus-core/src/test/java/dev/kske/eventbus/core/ExceptionTest.java

@@ -6,11 +6,11 @@ import org.junit.jupiter.api.Test;
 
 /**
  * Tests the dispatching of an exception event if an event handler threw an exception.
- * 
+ *
  * @author Kai S. K. Engelbart
  * @since 1.1.0
  */
-class ExceptionTest {
+public class ExceptionTest {
 
 	EventBus			bus			= new EventBus();
 	String				event		= "This event will cause an exception";
@@ -19,11 +19,11 @@ class ExceptionTest {
 
 	/**
 	 * Tests exception event delivery.
-	 * 
+	 *
 	 * @since 1.1.0
 	 */
 	@Test
-	void testExceptionEvent() {
+	public void testExceptionEvent() {
 		bus.registerListener(this);
 		bus.registerListener(new ExceptionListener());
 		bus.dispatch(event);
@@ -34,11 +34,11 @@ class ExceptionTest {
 	/**
 	 * Tests how the event bus reacts to an unhandled exception event. This should not lead to an
 	 * exception or an endless recursion and should be logged instead.
-	 * 
+	 *
 	 * @since 1.1.0
 	 */
 	@Test
-	void testUnhandledExceptionEvent() {
+	public void testUnhandledExceptionEvent() {
 		bus.registerListener(this);
 		bus.dispatch(event);
 		bus.removeListener(this);

event-bus-core/src/test/java/dev/kske/eventbus/core/NestedTest.java

@@ -0,0 +1,73 @@
+package dev.kske.eventbus.core;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.*;
+
+/**
+ * Tests nested event dispatches.
+ *
+ * @author Kai S. K. Engelbart
+ * @since 1.2.0
+ */
+public class NestedTest {
+
+	EventBus	bus;
+	boolean		nestedHit;
+
+	/**
+	 * Constructs an event bus and registers this test instance as an event listener.
+	 *
+	 * @since 1.2.0
+	 */
+	@BeforeEach
+	public void registerListener() {
+		bus = new EventBus();
+		bus.registerListener(this);
+	}
+
+	/**
+	 * Dispatches a simple event, which should in turn cause a string to be dispatched as a nested
+	 * event. If the corresponding handler sets {@link #nestedHit} to {@code true}, the test is
+	 * successful.
+	 *
+	 * @since 1.2.0
+	 */
+	@Test
+	public void testNestedDispatch() {
+		bus.dispatch(new SimpleEvent());
+		assertTrue(nestedHit);
+	}
+
+	/**
+	 * Dispatches a string as a nested event and cancels the current dispatch afterwards.
+	 *
+	 * @since 1.2.0
+	 */
+	@Event(SimpleEvent.class)
+	void onSimpleEvent() {
+		bus.dispatch("Nested event");
+		bus.cancel();
+	}
+
+	/**
+	 * Sets {@link #nestedHit} to {@code true} indicating that nested dispatches work.
+	 *
+	 * @since 1.2.0
+	 */
+	@Event(String.class)
+	void onString() {
+		nestedHit = true;
+	}
+
+	/**
+	 * Fails the test if an exception is caused during the dispatch.
+	 *
+	 * @param e the event containing the exception
+	 * @since 1.2.0
+	 */
+	@Event
+	void onException(ExceptionEvent e) {
+		fail("Exception during dispatch", e.getCause());
+	}
+}

pom.xml

@@ -9,7 +9,7 @@
 	<packaging>pom</packaging>
 
 	<name>Event Bus</name>
-	<description>An event handling framework for Java utilizing annotations.</description>
+	<description>An event handling library for Java utilizing annotations.</description>
 	<url>https://git.kske.dev/kske/event-bus</url>
 
 	<modules>
@@ -120,6 +120,28 @@
 						</goals>
 					</execution>
 				</executions>
+
+				<!-- Support JDK-style Javadoc tags -->
+				<configuration>
+					<tags>
+						<tag>
+							<name>apiNote</name>
+							<placement>a</placement>
+							<head>API Note:</head>
+						</tag>
+						<tag>
+							<name>implSpec</name>
+							<placement>a</placement>
+							<head>Implementation Requirements:</head>
+						</tag>
+						<tag>
+							<name>implNote</name>
+							<placement>a</placement>
+							<head>Implementation Note:</head>
+						</tag>
+					</tags>
+				</configuration>
+
 			</plugin>
 
 			<!-- GPG sign JAR -->