diff --git a/patterns/hexagonal-design-pattern/src/main/java/com/baeldung/hexagonal/core/contract/UserDataAdapter.java b/patterns/hexagonal-design-pattern/src/main/java/com/baeldung/hexagonal/core/contract/UserDataAdapter.java
new file mode 100644
index 0000000000..b89410e139
--- /dev/null
+++ b/patterns/hexagonal-design-pattern/src/main/java/com/baeldung/hexagonal/core/contract/UserDataAdapter.java
@@ -0,0 +1,12 @@
+package com.baeldung.hexagonal.core.contract;
+
+import com.baeldung.hexagonal.core.contract.dto.UserDTO;
+
+import java.util.List;
+
+public interface UserDataAdapter {
+
+    void addUser(UserDTO user);
+
+    List<UserDTO> getUsers();
+}
\ No newline at end of file