Add mediator design pattern with test case (#58)

Author: mperor

DesignPatterns/README.md

@@ -12,6 +12,7 @@ with practical examples and best practices for using design patterns to create r
 - [Chain of Responsibility](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility) 🔗
 - [Command](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command) 📝
 - [Execute Around Method (EAM)](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/eam) ⭕
+- [Mediator](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/mediator) 🗣️
 - [Memento](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/memento) 💾
 - [Observer](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/observer) 👀
 - [State](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/state) 📜

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/mediator/ChatRoom.java

@@ -0,0 +1,20 @@
+package pl.mperor.lab.java.design.pattern.behavioral.mediator;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Predicate;
+
+class ChatRoom {
+
+ private final List<ChatUser> users = new ArrayList<>();
+
+ void addUser(ChatUser user) {
+ users.add(user);
+ }
+
+ void sendMessage(String message, ChatUser sender) {
+ users.stream()
+ .filter(Predicate.not(sender::equals))
+ .forEach(user -> user.receive(message));
+ }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/mediator/ChatUser.java

@@ -0,0 +1,13 @@
+package pl.mperor.lab.java.design.pattern.behavioral.mediator;
+
+record ChatUser(ChatRoom mediator, String name) {
+
+ void send(String message) {
+ System.out.println(name + " sends: " + message);
+ mediator.sendMessage(message, this);
+ }
+
+ void receive(String message) {
+ System.out.println(name + " received: " + message);
+ }
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/mediator/ChatMediatorTest.java

@@ -0,0 +1,31 @@
+package pl.mperor.lab.java.design.pattern.behavioral.mediator;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import pl.mperor.lab.common.TestUtils;
+
+public class ChatMediatorTest {
+
+ @Test
+ public void testChatRoomMediating() {
+ var out = TestUtils.setTempSystemOut();
+
+ var chat = new ChatRoom();
+ var alice = new ChatUser(chat, "👩 Alice");
+ var bob = new ChatUser(chat, "👨 Bob");
+
+ chat.addUser(alice);
+ chat.addUser(bob);
+
+ alice.send("Hello everyone!");
+ bob.send("Hi Alice!");
+
+ var outLines = out.lines();
+ Assertions.assertEquals("👩 Alice sends: Hello everyone!", outLines.getFirst());
+ Assertions.assertEquals("👨 Bob received: Hello everyone!", outLines.getSecond());
+ Assertions.assertEquals("👨 Bob sends: Hi Alice!", outLines.getThird());
+ Assertions.assertEquals("👩 Alice received: Hi Alice!", outLines.getForth());
+
+ TestUtils.resetSystemOut();
+ }
+}