Add custom Event support.

src/org/apollo/game/model/entity/event/Event.java

@@ -0,0 +1,10 @@
+package org.apollo.game.model.entity.event;
+
+/**
+ * A type of event that may occur in the game world.
+ *
+ * @author Major
+ */
+public abstract class Event {
+
+}

src/org/apollo/game/model/entity/event/EventContext.java

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+package org.apollo.game.model.entity.event;
+
+/**
+ * The context of an {@link Event}.
+ *
+ * @author Major
+ */
+final class EventContext {
+
+	/**
+	 * Indicates whether or not the Event chain has been terminated.
+	 */
+	private boolean terminated;
+
+	/**
+	 * Terminates the Event chain.
+	 */
+	public void terminate() {
+		terminated = true;
+	}
+
+	/**
+	 * Returns whether or not the Event chain has been terminated.
+	 * 
+	 * @return {@code true} if the Event chain has been terminated, otherwise {@code false}.
+	 */
+	public boolean terminated() {
+		return terminated;
+	}
+
+}

src/org/apollo/game/model/entity/event/EventListener.java

@@ -0,0 +1,21 @@
+package org.apollo.game.model.entity.event;
+
+/**
+ * A listener for an {@link Event} that may occur in the game world.
+ *
+ * @author Major
+ *
+ * @param <E> The type of Event.
+ */
+@FunctionalInterface
+public interface EventListener<E> {
+
+	/**
+	 * Handles the {@link Event} that occurred.
+	 * 
+	 * @param event The Event.
+	 * @param context The {@link EventContext}.
+	 */
+	public void handle(E event, EventContext context);
+
+}

src/org/apollo/game/model/entity/event/EventListenerChain.java

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+package org.apollo.game.model.entity.event;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A chain of {@link EventListener}s.
+ *
+ * @author Major
+ * @param <E> The type of {@link Event} the listeners in this chain listen for.
+ */
+final class EventListenerChain<E extends Event> {
+
+	/**
+	 * The List of EventListeners.
+	 */
+	private final List<EventListener<E>> listeners = new ArrayList<>();
+
+	/**
+	 * Adds an {@link EventListener} to this chain.
+	 * 
+	 * @param listener The EventListener to add.
+	 */
+	public void addListener(EventListener<E> listener) {
+		listeners.add(listener);
+	}
+
+	/**
+	 * Notifies each {@link EventListener} in this chain that an {@link Event} has occurred.
+	 * 
+	 * @param event The event.
+	 * @return {@code true} if the Event should continue on with its outcome, {@code false} if not.
+	 */
+	public boolean notify(E event) {
+		EventContext context = new EventContext();
+		for (EventListener<E> listener : listeners) {
+			listener.handle(event, context);
+
+			if (context.terminated()) {
+				return false;
+			}
+		}
+
+		return false;
+	}
+
+}

src/org/apollo/game/model/entity/event/EventListenerChainSet.java

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+package org.apollo.game.model.entity.event;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A set of {@link EventListenerChain}s.
+ *
+ * @author Major
+ */
+public final class EventListenerChainSet {
+
+	/**
+	 * The Map of Event Classes to EventListenerChains.
+	 */
+	private final Map<Class<? extends Event>, EventListenerChain<? extends Event>> chains = new HashMap<>();
+
+	/**
+	 * Notifies the appropriate {@link EventListenerChain} that an {@link Event} has occurred.
+	 * 
+	 * @param event The Event.
+	 * @return {@code true} if the Event should continue on with its outcome, {@code false} if not.
+	 */
+	public <E extends Event> boolean notify(E event) {
+		@SuppressWarnings("unchecked")
+		EventListenerChain<E> chain = (EventListenerChain<E>) chains.get(event);
+		return chain.notify(event);
+	}
+
+	/**
+	 * Places the {@link EventListenerChain} into this set.
+	 * 
+	 * @param clazz The {@link Class} to associate the EventListenerChain with.
+	 * @param chain The EventListenerChain.
+	 */
+	public <E extends Event> void putListenerChain(Class<E> clazz, EventListenerChain<E> chain) {
+		chains.put(clazz, chain);
+	}
+
+}

src/org/apollo/game/model/entity/event/package-info.java

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+/**
+ * Contains event-related classes.
+ */
+package org.apollo.game.model.entity.event;