fix: check styles on publisher-subscriber design pattern (iluwatar#2898)

Author: sanurah

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/App.java

@@ -11,7 +11,39 @@
 import com.iluwatar.publish.subscribe.subscriber.Subscriber;
 import com.iluwatar.publish.subscribe.subscriber.WeatherSubscriber;
 
+/**
+ * <p>The Publish and Subscribe pattern is a messaging paradigm used in software architecture with
+ * several key points: <li>Decoupling of publishers and subscribers: Publishers and subscribers
+ * operate independently, and there's no direct link between them. This enhances the scalability and
+ * * modularity of applications.</li><li>Event-driven communication: The pattern facilitates
+ * event-driven architectures by allowing publishers to broadcast events without concerning
+ * themselves with who receives the events.</li><li>Dynamic subscription: Subscribers can
+ * dynamically choose to listen for specific events or messages they are interested in, often by
+ * subscribing to a particular topic or channel.</li><li>Asynchronous processing: The pattern
+ * inherently supports asynchronous message processing, enabling efficient handling of events and
+ * improving application responsiveness.</li><li>Scalability: By decoupling senders and receivers,
+ * the pattern can support a large number of publishers and subscribers, making it suitable for
+ * scalable systems.</li><li>Flexibility and adaptability: New subscribers or publishers can be
+ * added to the system without significant changes to the existing components, making the system
+ * highly adaptable to evolving requirements.</li></p>
+ *
+ * <p>In this example we will create two topics {@link TopicName} WEATHER and CUSTOMER_SUPPORT.
+ * then we will register those topics in {@link Publisher}
+ * we will create two {@link WeatherSubscriber} to WEATHER {@link Topic}
+ * we will create two {@link CustomerSupportSubscriber} to CUSTOMER_SUPPORT {@link Topic}
+ * then we will publish the two {@link Topic} with different content in the {@link Message}
+ * And we can observe the output in the log where,
+ * {@link WeatherSubscriber} publish the message with {@link WeatherContent}
+ * {@link CustomerSupportSubscriber} publish the message with {@link CustomerSupportContent}
+ * Each subscriber is only listening to the subscribed topic.
+ */
 public class App {
+
+  /**
+   * Program entry point.
+   *
+   * @param args command line args
+   */
   public static void main(String[] args) {
 
     final String weatherSub1Name = "weatherSub1";

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/model/CustomerSupportContent.java

@@ -1,5 +1,8 @@
 package com.iluwatar.publish.subscribe.model;
 
+/**
+ * This enum defines the content for {@link Topic} CUSTOMER_SUPPORT
+ */
 public enum CustomerSupportContent {
 
   DE("[email protected]"),

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/model/Message.java

@@ -1,4 +1,7 @@
 package com.iluwatar.publish.subscribe.model;
 
+/**
+ * This class represents a Message that holds the published content
+ */
 public record Message(Object content) {
 }

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/model/Topic.java

@@ -4,27 +4,55 @@
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArraySet;
 
+/**
+ * This class represents a Topic that topic name and subscribers
+ */
 public class Topic {
 
   private final TopicName name;
   private final Set<Subscriber> subscribers = new CopyOnWriteArraySet<>();
 
+  /**
+   * Creates a new instance of the Topic class.
+   *
+   * @param name The name of the topic.
+   */
   public Topic(TopicName name) {
     this.name = name;
   }
 
+  /**
+   * Get the name of the topic
+   *
+   * @return topic name
+   */
   public TopicName getName() {
     return name;
   }
 
+  /**
+   * Add a subscriber to the list of subscribers
+   *
+   * @param subscriber subscriber to add
+   */
   public void addSubscriber(Subscriber subscriber) {
     subscribers.add(subscriber);
   }
 
+  /**
+   * Remove a subscriber to the list of subscribers
+   *
+   * @param subscriber subscriber to remove
+   */
   public void removeSubscriber(Subscriber subscriber) {
     subscribers.remove(subscriber);
   }
 
+  /**
+   * Publish a message to subscribers
+   *
+   * @param message message with content to publish
+   */
   public void publish(Message message) {
     for (Subscriber subscriber : subscribers) {
       subscriber.onMessage(message);

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/model/TopicName.java

@@ -1,5 +1,8 @@
 package com.iluwatar.publish.subscribe.model;
 
+/**
+ * This enum defines the available topic names to be used in {@link Topic}
+ */
 public enum TopicName {
   WEATHER,
   CUSTOMER_SUPPORT

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/model/WeatherContent.java

@@ -1,5 +1,8 @@
 package com.iluwatar.publish.subscribe.model;
 
+/**
+ * This enum defines the content for {@link Topic} WEATHER
+ */
 public enum WeatherContent {
   earthquake("earthquake tsunami warning"),
   flood("flood start evacuation"),

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/publisher/Publisher.java

@@ -3,9 +3,23 @@
 import com.iluwatar.publish.subscribe.model.Message;
 import com.iluwatar.publish.subscribe.model.Topic;
 
+/**
+ * This class represents a Publisher
+ */
 public interface Publisher {
 
+    /**
+     * Register a topic in the publisher
+     *
+     * @param topic the topic to be registered
+     */
     void registerTopic(Topic topic);
 
+    /**
+     * Register a topic in the publisher
+     *
+     * @param topic the topic to publish the message under
+     * @param message message with content to be published
+     */
     void publish(Topic topic, Message message);
-}
+}

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/publisher/PublisherImpl.java

@@ -7,6 +7,9 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * This class is an implementation of the Publisher
+ */
 public class PublisherImpl implements Publisher {
 
   private static final Logger logger = LoggerFactory.getLogger(PublisherImpl.class);

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/subscriber/CustomerSupportSubscriber.java

@@ -2,9 +2,14 @@
 
 import com.iluwatar.publish.subscribe.model.CustomerSupportContent;
 import com.iluwatar.publish.subscribe.model.Message;
+import lombok.extern.slf4j.Slf4j;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * This class subscribes to CUSTOMER_SUPPORT topic
+ */
+@Slf4j
 public class CustomerSupportSubscriber implements Subscriber {
 
   private static final Logger logger = LoggerFactory.getLogger(CustomerSupportSubscriber.class);

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/subscriber/Subscriber.java

@@ -2,6 +2,15 @@
 
 import com.iluwatar.publish.subscribe.model.Message;
 
+/**
+ * This class represents a Subscriber
+ */
 public interface Subscriber {
+
+  /**
+   * On message method will trigger when the subscribed event is published
+   *
+   * @param message the message contains the content of the published event
+   */
   void onMessage(Message message);
 }

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/subscriber/WeatherSubscriber.java

@@ -7,6 +7,9 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * This class subscribes to WEATHER topic
+ */
 @Slf4j
 public class WeatherSubscriber implements Subscriber {