Implement an event handler

src/main/java/emu/grasscutter/server/event/Cancellable.java

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+package emu.grasscutter.server.event;
+
+/**
+ * Implementing this interface marks an event as cancellable.
+ */
+public interface Cancellable {
+    void cancel();
+}

src/main/java/emu/grasscutter/server/event/Event.java

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+package emu.grasscutter.server.event;
+
+import emu.grasscutter.Grasscutter;
+
+/**
+ * A generic server event.
+ */
+public abstract class Event {
+    private boolean cancelled = false;
+
+    /**
+     * Return the cancelled state of the event.
+     */
+    public boolean isCanceled() {
+        return this.cancelled;
+    }
+
+    /**
+     * Cancels the event if possible.
+     */
+    public void cancel() throws IllegalAccessException {
+        if(!(this instanceof Cancellable))
+            throw new IllegalAccessException("Event is not cancellable.");
+        this.cancelled = true;
+    }
+
+    /**
+     * Pushes this event to all listeners.
+     */
+    public void call() {
+        Grasscutter.getPluginManager().invokeEvent(this);
+    }
+}

src/main/java/emu/grasscutter/server/event/EventHandler.java

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+package emu.grasscutter.server.event;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Declares a class as an event listener/handler.
+ */
+@Retention(RetentionPolicy.RUNTIME)
+public @interface EventHandler {
+}

src/main/java/emu/grasscutter/server/event/Listener.java

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+package emu.grasscutter.server.event;
+
+/**
+ * Implementing this interface declares a class as an event listener.
+ */
+public interface Listener {
+}

src/main/java/emu/grasscutter/server/event/ServerEvent.java

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+package emu.grasscutter.server.event;
+
+/**
+ * An event that is related to the internals of the server.
+ */
+public abstract class ServerEvent extends Event {
+    protected final Type type;
+    
+    public ServerEvent(Type type) {
+        this.type = type;
+    }
+    
+    public enum Type {
+        DISPATCH,
+        GAME
+    }
+}