Add all 23 GoF design pattern implementations

01-creational/factory-method/NotificationService.java

@@ -0,0 +1,24 @@
+package factorymethod;
+
+public class NotificationService {
+
+    public void send(String type, String recipient, String message) {
+
+        // Creation logic mixed with business logic
+        Notification notification;
+        if ("EMAIL".equals(type)) {
+            notification = new EmailNotification();
+        } else if ("SMS".equals(type)) {
+            notification = new SmsNotification();
+        } else if ("PUSH".equals(type)) {
+            notification = new PushNotification();
+        } else {
+            throw new IllegalArgumentException("Unknown type: " + type);
+        }
+
+        // Business logic that should never change
+        System.out.println("Sending " + type + " to " + recipient);
+        notification.send(recipient, message);
+        System.out.println("Delivered.");
+    }
+}