add comments

src/main/java/com/github/nkzawa/emitter/Emitter.java

@@ -7,6 +7,12 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ConcurrentMap;
 
+
+/**
+ * The event emitter which is ported from the JavaScript module.
+ *
+ * @see <a href="https://github.com/component/emitter">https://github.com/component/emitter</a>
+ */
 public class Emitter {
 
     private ConcurrentMap<String, ConcurrentLinkedQueue<Listener>> callbacks
@@ -15,6 +21,12 @@ public class Emitter {
     private ConcurrentMap<Listener, Listener> onceCallbacks = new ConcurrentHashMap<Listener, Listener>();
 
 
+    /**
+     * Listens on the event.
+     * @param event event name.
+     * @param fn
+     * @return a reference to to this object.
+     */
     public Emitter on(String event, Listener fn) {
         ConcurrentLinkedQueue<Listener> callbacks = this.callbacks.get(event);
         if (callbacks == null) {
@@ -28,6 +40,13 @@ public class Emitter {
         return this;
     }
 
+    /**
+     * Adds a one time listener for the event.
+     *
+     * @param event
+     * @param fn
+     * @return a reference to to this object.
+     */
     public Emitter once(final String event, final Listener fn) {
         Listener on = new Listener() {
             @Override
@@ -42,12 +61,23 @@ public class Emitter {
         return this;
     }
 
+    /**
+     * Removes all registered listeners.
+     *
+     * @return a reference to to this object.
+     */
     public Emitter off() {
         this.callbacks.clear();
         this.onceCallbacks.clear();
         return this;
     }
 
+    /**
+     * Removes all listeners of the specified event.
+     *
+     * @param event
+     * @return a reference to to this object.
+     */
     public Emitter off(String event) {
         ConcurrentLinkedQueue<Listener> callbacks = this.callbacks.remove(event);
         if (callbacks != null) {
@@ -58,6 +88,13 @@ public class Emitter {
         return this;
     }
 
+    /**
+     * Removes the listener.
+     *
+     * @param event
+     * @param fn
+     * @return a reference to to this object.
+     */
     public Emitter off(String event, Listener fn) {
         ConcurrentLinkedQueue<Listener> callbacks = this.callbacks.get(event);
         if (callbacks != null) {
@@ -67,6 +104,13 @@ public class Emitter {
         return this;
     }
 
+    /**
+     * Executes each of listeners with the given args.
+     *
+     * @param event
+     * @param args
+     * @return a reference to to this object.
+     */
     public Emitter emit(String event, Object... args) {
         ConcurrentLinkedQueue<Listener> callbacks = this.callbacks.get(event);
         if (callbacks != null) {
@@ -78,12 +122,24 @@ public class Emitter {
         return this;
     }
 
+    /**
+     * Returns a list of listeners for the specified event.
+     *
+     * @param event
+     * @return a reference to to this object.
+     */
     public List<Listener> listeners(String event) {
         ConcurrentLinkedQueue<Listener> callbacks = this.callbacks.get(event);
         return callbacks != null ?
                 new ArrayList<Listener>(callbacks) : new ArrayList<Listener>();
     }
 
+    /**
+     * Check if this emitter has listeners for the specified event.
+     *
+     * @param event
+     * @return a reference to to this object.
+     */
     public boolean hasListeners(String event) {
         return !this.listeners(event).isEmpty();
     }