Add Dependency Inversion Principle (DIP) example (1/3)

JavierCane · JavierCane · commit a290fe48a264 · 2018-06-21T10:51:59.000+02:00
* Add the first stage or iteration of our code. A `UserSearcher` use case instantiating the `HardcodedInMemoryUsersRepository` collaborator while initializing its class attributes. This is how we illustrate high coupling between classes.
diff --git a/src/main/java/tv/codely/solid_principles/dependency_inversion_principle/User.java b/src/main/java/tv/codely/solid_principles/dependency_inversion_principle/User.java
@@ -0,0 +1,28 @@
+package tv.codely.solid_principles.dependency_inversion_principle;
+
+import java.util.Objects;
+
+final public class User {
+    private Integer id;
+    private String name;
+
+    public User(Integer id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (this == other) return true;
+
+        if (!(other instanceof User)) return false;
+
+        User otherUser = (User) other;
+        return Objects.equals(id, otherUser.id) && Objects.equals(name, otherUser.name);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, name);
+    }
+}
diff --git a/src/main/java/tv/codely/solid_principles/dependency_inversion_principle/stage_1_instantiating_from_clients/HardcodedInMemoryUsersRepository.java b/src/main/java/tv/codely/solid_principles/dependency_inversion_principle/stage_1_instantiating_from_clients/HardcodedInMemoryUsersRepository.java
@@ -0,0 +1,21 @@
+package tv.codely.solid_principles.dependency_inversion_principle.stage_1_instantiating_from_clients;
+
+import tv.codely.solid_principles.dependency_inversion_principle.User;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+final class HardcodedInMemoryUsersRepository {
+    private Map<Integer, User> users = Collections.unmodifiableMap(new HashMap<Integer, User>() {
+        {
+            put(1, new User(1, "Rafa"));
+            put(2, new User(2, "Javi"));
+        }
+    });
+
+    public Optional<User> search(Integer id) {
+        return Optional.ofNullable(users.get(id));
+    }
+}
diff --git a/src/main/java/tv/codely/solid_principles/dependency_inversion_principle/stage_1_instantiating_from_clients/UserSearcher.java b/src/main/java/tv/codely/solid_principles/dependency_inversion_principle/stage_1_instantiating_from_clients/UserSearcher.java
@@ -0,0 +1,13 @@
+package tv.codely.solid_principles.dependency_inversion_principle.stage_1_instantiating_from_clients;
+
+import tv.codely.solid_principles.dependency_inversion_principle.User;
+
+import java.util.Optional;
+
+final class UserSearcher {
+    private HardcodedInMemoryUsersRepository usersRepository = new HardcodedInMemoryUsersRepository();
+
+    public Optional<User> search(Integer id) {
+        return usersRepository.search(id);
+    }
+}
diff --git a/src/test/java/tv/codely/solid_principles/dependency_inversion_principle/stage_1_instantiating_from_clients/UserSearcherShould.java b/src/test/java/tv/codely/solid_principles/dependency_inversion_principle/stage_1_instantiating_from_clients/UserSearcherShould.java
@@ -0,0 +1,32 @@
+package tv.codely.solid_principles.dependency_inversion_principle.stage_1_instantiating_from_clients;
+
+import org.junit.jupiter.api.Test;
+import tv.codely.solid_principles.dependency_inversion_principle.User;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+final class UserSearcherShould {
+    @Test
+    void find_existing_users() {
+        // We would be coupled to the actual HardcodedInMemoryUsersRepository implementation.
+        // We don't have the option to set test users as we would have to do if we had a real database repository.
+        Integer existingUserId = 1;
+        UserSearcher userSearcher = new UserSearcher();
+
+        Optional<User> expectedUser = Optional.of(new User(1, "Rafa"));
+
+        assertEquals(expectedUser, userSearcher.search(existingUserId));
+    }
+
+    @Test
+    void not_find_non_existing_users() {
+        Integer nonExistingUserId = 5;
+        UserSearcher userSearcher = new UserSearcher();
+
+        Optional<User> expectedEmptyResult = Optional.empty();
+
+        assertEquals(expectedEmptyResult, userSearcher.search(nonExistingUserId));
+    }
+}
