From 002180ed3b37162c527358bd7bfc86b8d274ad5c Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Mon, 15 Feb 2021 14:43:34 +0100
Subject: [PATCH] Remove EventListener and IEvent marker interfaces

This allows Event Bus to interface with existing classes without
modification.
---
 README.md                                     | 13 +++----
 .../dev/kske/eventbus/ap/EventProcessor.java  | 13 +------
 .../java/dev/kske/eventbus/core/Event.java    |  7 ++--
 .../java/dev/kske/eventbus/core/EventBus.java | 16 ++++-----
 .../dev/kske/eventbus/core/EventHandler.java  | 34 +++++++------------
 .../dev/kske/eventbus/core/EventListener.java | 12 -------
 .../java/dev/kske/eventbus/core/IEvent.java   | 12 -------
 .../dev/kske/eventbus/core/CancelTest.java    |  2 +-
 .../dev/kske/eventbus/core/DispatchTest.java  |  4 +--
 .../dev/kske/eventbus/core/SimpleEvent.java   |  2 +-
 10 files changed, 33 insertions(+), 82 deletions(-)
 delete mode 100644 event-bus-core/src/main/java/dev/kske/eventbus/core/EventListener.java
 delete mode 100644 event-bus-core/src/main/java/dev/kske/eventbus/core/IEvent.java

diff --git a/README.md b/README.md
index c6e2888..8666ba8 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 ## Introduction
 
 This library allows passing events between different objects without them having a direct reference to each other.
-Any class can be made an event by implementing the `IEvent` interface.
+Any object can serve as an event.
 
 Using an instance of the `EventBus` class, an instant of the event class can be dispatched.
 This means that it will be forwarded to all listeners registered for it at the event bus.
@@ -13,16 +13,13 @@ In addition, a singleton instance of the event bus is provided by the `EventBus#
 To listen to events, register event handling methods using the `Event` annotation.
 For this to work, the method must have a return type of `void` and declare a single parameter of the desired event type.
 Alternatively, a parameter-less event handler can be declared as shown [below](#parameter-less-event-handlers).
-Additionally, the class containing the method must implement the `EventListener` interface.
 
 ## A Simple Example
 
-Lets look at a simple example: we declare the empty class `SimpleEvent` that implements `IEvent` and can thus be used as an event.
+Lets look at a simple example: we declare the empty class `SimpleEvent` whose objects can be used as events.
 
 ```java
-import dev.kske.eventbus.core.IEvent;
-
-public class SimpleEvent implements IEvent {}
+public class SimpleEvent {}
 ```
 
 Next, an event listener for the `SimpleEvent` is declared:
@@ -30,7 +27,7 @@ Next, an event listener for the `SimpleEvent` is declared:
 ```java
 import dev.kske.eventbus.core.*;
 
-public class SimpleEventListener implements EventListener {
+public class SimpleEventListener {
 
     public SimpleEventListener() {
 
@@ -165,7 +162,7 @@ opens my.module to dev.kske.eventbus.core;
 To assist you with writing event listeners, the Event Bus AP (Annotation Processor) module enforces correct usage of the `@Event` annotation during compile time.
 This reduces difficult-to-debug bugs that occur during runtime to compile-time errors which can be easily fixed.
 
-The event annotation processor detects invalid event handlers, missing `EventListener` implementations, event type issues with more to come in future versions.
+The event annotation processor detects invalid event handlers and event type issues with more to come in future versions.
 
 When using Maven, it can be registered using the Maven Compiler Plugin:
 
diff --git a/event-bus-ap/src/main/java/dev/kske/eventbus/ap/EventProcessor.java b/event-bus-ap/src/main/java/dev/kske/eventbus/ap/EventProcessor.java
index c05f15f..f6cc75d 100644
--- a/event-bus-ap/src/main/java/dev/kske/eventbus/ap/EventProcessor.java
+++ b/event-bus-ap/src/main/java/dev/kske/eventbus/ap/EventProcessor.java
@@ -34,8 +34,7 @@ public class EventProcessor extends AbstractProcessor {
 
 	private void processRound(Set<ExecutableElement> eventHandlers) {
 		for (ExecutableElement eventHandler : eventHandlers) {
-			TypeElement	eventListener	= (TypeElement) eventHandler.getEnclosingElement();
-			Event		eventAnnotation	= eventHandler.getAnnotation(Event.class);
+			Event eventAnnotation = eventHandler.getAnnotation(Event.class);
 
 			// Determine how the event type is defined
 			boolean useParameter;
@@ -68,11 +67,6 @@ public class EventProcessor extends AbstractProcessor {
 			var	paramElement	= eventHandler.getParameters().get(0);
 			var	paramType		= paramElement.asType();
 
-			// Check for valid event type
-			if (useParameter && !processingEnv.getTypeUtils().isAssignable(paramType,
-				getTypeMirror(IEvent.class)))
-				error(paramElement, "Parameter must implement IEvent");
-
 			// Check for handlers for abstract types that aren't polymorphic
 			if (eventHandler.getAnnotation(Polymorphic.class) == null
 				&& paramType.getKind() == TypeKind.DECLARED) {
@@ -82,11 +76,6 @@ public class EventProcessor extends AbstractProcessor {
 					warning(paramElement,
 						"Parameter should be instantiable or handler should use @Polymorphic");
 			}
-
-			// Check listener for interface implementation
-			if (!eventListener.getInterfaces().contains(getTypeMirror(EventListener.class)))
-				warning(eventHandler.getEnclosingElement(),
-					"Class should implement EventListener interface");
 		}
 	}
 
diff --git a/event-bus-core/src/main/java/dev/kske/eventbus/core/Event.java b/event-bus-core/src/main/java/dev/kske/eventbus/core/Event.java
index 7a6b837..743c803 100644
--- a/event-bus-core/src/main/java/dev/kske/eventbus/core/Event.java
+++ b/event-bus-core/src/main/java/dev/kske/eventbus/core/Event.java
@@ -9,10 +9,9 @@ import java.lang.annotation.*;
  * Indicates that a method is an event handler. To be successfully used as such, the method has to
  * comply with the following specifications:
  * <ul>
- * <li>Declared inside a class that implements {@link EventListener}</li>
  * <li>Specifying an event type by either
  * <ul>
- * <li>Declaring one parameter of a type that implements {@link IEvent}</li>
+ * <li>Declaring one object parameter</li>
  * <li>Defining the class of the event using the annotation value</li>
  * </ul>
  * </li>
@@ -38,7 +37,7 @@ public @interface Event {
 	 * @return the event type accepted by the handler
 	 * @since 1.0.0
 	 */
-	Class<? extends IEvent> value() default USE_PARAMETER.class;
+	Class<?> value() default USE_PARAMETER.class;
 
 	/**
 	 * Signifies that the event type the handler listens to is determined by the type of its only
@@ -46,5 +45,5 @@ public @interface Event {
 	 *
 	 * @since 0.0.3
 	 */
-	static final class USE_PARAMETER implements IEvent {}
+	static final class USE_PARAMETER {}
 }
diff --git a/event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java b/event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java
index 40ed4fa..8f30e89 100644
--- a/event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java
+++ b/event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java
@@ -51,11 +51,11 @@ public final class EventBus {
 		return instance;
 	}
 
-	private final Map<Class<? extends IEvent>, TreeSet<EventHandler>>	bindings			=
+	private final Map<Class<?>, TreeSet<EventHandler>>	bindings			=
 		new ConcurrentHashMap<>();
-	private final Set<EventListener>									registeredListeners	=
+	private final Set<Object>							registeredListeners	=
 		ConcurrentHashMap.newKeySet();
-	private final ThreadLocal<DispatchState>							dispatchState		=
+	private final ThreadLocal<DispatchState>			dispatchState		=
 		ThreadLocal.withInitial(DispatchState::new);
 
 	/**
@@ -65,7 +65,7 @@ public final class EventBus {
 	 * @param event the event to dispatch
 	 * @since 0.0.1
 	 */
-	public void dispatch(IEvent event) {
+	public void dispatch(Object event) {
 		Objects.requireNonNull(event);
 		logger.log(Level.INFO, "Dispatching event {0}", event);
 
@@ -95,7 +95,7 @@ public final class EventBus {
 	 * @return all event handlers registered for the event class
 	 * @since 0.0.1
 	 */
-	private List<EventHandler> getHandlersFor(Class<? extends IEvent> eventClass) {
+	private List<EventHandler> getHandlersFor(Class<?> eventClass) {
 
 		// Get handlers defined for the event class
 		Set<EventHandler> handlers = bindings.getOrDefault(eventClass, new TreeSet<>());
@@ -133,7 +133,7 @@ public final class EventBus {
 	 * @since 0.0.1
 	 * @see Event
 	 */
-	public void registerListener(EventListener listener) throws EventBusException {
+	public void registerListener(Object listener) throws EventBusException {
 		Objects.requireNonNull(listener);
 		if (registeredListeners.contains(listener))
 			throw new EventBusException(listener + " already registered!");
@@ -170,7 +170,7 @@ public final class EventBus {
 	 * @param listener the listener to remove
 	 * @since 0.0.1
 	 */
-	public void removeListener(EventListener listener) {
+	public void removeListener(Object listener) {
 		Objects.requireNonNull(listener);
 		logger.log(Level.INFO, "Removing event listener {0}", listener.getClass().getName());
 
@@ -204,7 +204,7 @@ public final class EventBus {
 	 * @return all registered event listeners
 	 * @since 0.0.1
 	 */
-	public Set<EventListener> getRegisteredListeners() {
+	public Set<Object> getRegisteredListeners() {
 		return Collections.unmodifiableSet(registeredListeners);
 	}
 }
diff --git a/event-bus-core/src/main/java/dev/kske/eventbus/core/EventHandler.java b/event-bus-core/src/main/java/dev/kske/eventbus/core/EventHandler.java
index 16b4561..f1bbea3 100644
--- a/event-bus-core/src/main/java/dev/kske/eventbus/core/EventHandler.java
+++ b/event-bus-core/src/main/java/dev/kske/eventbus/core/EventHandler.java
@@ -21,12 +21,12 @@ final class EventHandler implements Comparable<EventHandler> {
 	 */
 	public static final int DEFAULT_PRIORITY = 100;
 
-	private final EventListener				listener;
-	private final Method					method;
-	private final Class<? extends IEvent>	eventType;
-	private final boolean					useParameter;
-	private final boolean					polymorphic;
-	private final int						priority;
+	private final Object	listener;
+	private final Method	method;
+	private final Class<?>	eventType;
+	private final boolean	useParameter;
+	private final boolean	polymorphic;
+	private final int		priority;
 
 	/**
 	 * Constructs an event handler.
@@ -38,8 +38,7 @@ final class EventHandler implements Comparable<EventHandler> {
 	 *                           specification
 	 * @since 0.0.1
 	 */
-	@SuppressWarnings("unchecked")
-	EventHandler(EventListener listener, Method method, Event annotation) throws EventBusException {
+	EventHandler(Object listener, Method method, Event annotation) throws EventBusException {
 		this.listener	= listener;
 		this.method		= method;
 		useParameter	= annotation.value() == USE_PARAMETER.class;
@@ -57,17 +56,8 @@ final class EventHandler implements Comparable<EventHandler> {
 		if (!method.getReturnType().equals(void.class))
 			throw new EventBusException(method + " does not have a return type of void!");
 
-		// Determine the event type
-		if (useParameter) {
-			var param = method.getParameterTypes()[0];
-			if (!IEvent.class.isAssignableFrom(param))
-				throw new EventBusException(param + " is not of type IEvent!");
-			eventType = (Class<? extends IEvent>) param;
-		} else {
-			eventType = annotation.value();
-		}
-
-		// Determine additional handler properties
+		// Determine handler properties
+		eventType	= useParameter ? method.getParameterTypes()[0] : annotation.value();
 		polymorphic	= method.isAnnotationPresent(Polymorphic.class);
 		priority	= method.isAnnotationPresent(Priority.class)
 			? method.getAnnotation(Priority.class).value()
@@ -107,7 +97,7 @@ final class EventHandler implements Comparable<EventHandler> {
 	 * @throws EventBusException if the handler throws an exception
 	 * @since 0.0.1
 	 */
-	void execute(IEvent event) throws EventBusException {
+	void execute(Object event) throws EventBusException {
 		try {
 			if (useParameter)
 				method.invoke(listener, event);
@@ -122,13 +112,13 @@ final class EventHandler implements Comparable<EventHandler> {
 	 * @return the listener containing this handler
 	 * @since 0.0.1
 	 */
-	EventListener getListener() { return listener; }
+	Object getListener() { return listener; }
 
 	/**
 	 * @return the event type this handler listens for
 	 * @since 0.0.3
 	 */
-	Class<? extends IEvent> getEventType() { return eventType; }
+	Class<?> getEventType() { return eventType; }
 
 	/**
 	 * @return the priority of this handler
diff --git a/event-bus-core/src/main/java/dev/kske/eventbus/core/EventListener.java b/event-bus-core/src/main/java/dev/kske/eventbus/core/EventListener.java
deleted file mode 100644
index 4e54505..0000000
--- a/event-bus-core/src/main/java/dev/kske/eventbus/core/EventListener.java
+++ /dev/null
@@ -1,12 +0,0 @@
-package dev.kske.eventbus.core;
-
-/**
- * Marker interface for event listeners. Event listeners can contain event handling methods to which
- * events can be dispatched.
- *
- * @author Kai S. K. Engelbart
- * @since 0.0.1
- * @see Event
- * @see EventBus
- */
-public interface EventListener {}
diff --git a/event-bus-core/src/main/java/dev/kske/eventbus/core/IEvent.java b/event-bus-core/src/main/java/dev/kske/eventbus/core/IEvent.java
deleted file mode 100644
index bb09b18..0000000
--- a/event-bus-core/src/main/java/dev/kske/eventbus/core/IEvent.java
+++ /dev/null
@@ -1,12 +0,0 @@
-package dev.kske.eventbus.core;
-
-/**
- * Marker interface for event objects. Event objects can be used as event handler parameters and
- * thus can be dispatched to the event bus.
- *
- * @author Kai S. K. Engelbart
- * @since 0.0.1
- * @see Event
- * @see EventBus
- */
-public interface IEvent {}
diff --git a/event-bus-core/src/test/java/dev/kske/eventbus/core/CancelTest.java b/event-bus-core/src/test/java/dev/kske/eventbus/core/CancelTest.java
index cde0128..5f715c7 100644
--- a/event-bus-core/src/test/java/dev/kske/eventbus/core/CancelTest.java
+++ b/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 implements EventListener {
+class CancelTest {
 
 	EventBus	bus;
 	int			hits;
diff --git a/event-bus-core/src/test/java/dev/kske/eventbus/core/DispatchTest.java b/event-bus-core/src/test/java/dev/kske/eventbus/core/DispatchTest.java
index 3fb1a3b..95bae3f 100644
--- a/event-bus-core/src/test/java/dev/kske/eventbus/core/DispatchTest.java
+++ b/event-bus-core/src/test/java/dev/kske/eventbus/core/DispatchTest.java
@@ -10,7 +10,7 @@ import org.junit.jupiter.api.*;
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-class DispatchTest implements EventListener {
+class DispatchTest {
 
 	EventBus	bus;
 	static int	hits;
@@ -27,7 +27,7 @@ class DispatchTest implements EventListener {
 	}
 
 	/**
-	 * Tests {@link EventBus#dispatch(IEvent)} with multiple handler priorities, a subtype handler
+	 * Tests {@link EventBus#dispatch(Object)} with multiple handler priorities, a subtype handler
 	 * and a static handler.
 	 *
 	 * @since 0.0.1
diff --git a/event-bus-core/src/test/java/dev/kske/eventbus/core/SimpleEvent.java b/event-bus-core/src/test/java/dev/kske/eventbus/core/SimpleEvent.java
index ede1afa..bed60bc 100644
--- a/event-bus-core/src/test/java/dev/kske/eventbus/core/SimpleEvent.java
+++ b/event-bus-core/src/test/java/dev/kske/eventbus/core/SimpleEvent.java
@@ -6,4 +6,4 @@ package dev.kske.eventbus.core;
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-public class SimpleEvent implements IEvent {}
+public class SimpleEvent {}