Do homework.

src/main/java/mate/academy/service/AuthenticationService.java

@@ -1,16 +1,19 @@
 package mate.academy.service;
 
 public class AuthenticationService {
-    /**
-     * Imagine that some user wants to login to your site.
-     * You should check if user credentials (login and password) are valid or not.
-     * All users are stored in <code>UserService</code> class.
-     * @param email - user's email
-     * @param password - user's password
-     * @return true if user by email exists and passed password is equal to user's password.
-     * Return false in any other cases.
-     */
     public boolean login(String email, String password) {
-        return false;
+        UserService userService = new UserService();
+        return userService.findByEmail(email)
+                .map(user -> user.getPassword().equals(password))
+                .orElse(false);
     }
 }
+
+
+//        User user = userService.findByEmail(email);
+//        return userService.findByEmail(email) != null
+//        ? user.getPassword().equals(password) : false;
+
+//        return Optional.ofNullable(userService.findByEmail(email))
+//                .map(user -> user.getPassword().equals(password))
+//                .orElse(false);

src/main/java/mate/academy/service/UserService.java

@@ -1,5 +1,7 @@
 package mate.academy.service;
 
+import java.util.Arrays;
+import java.util.Optional;
 import mate.academy.model.User;
 
 public class UserService {
@@ -8,13 +10,20 @@ public class UserService {
             new User("[email protected]", "1234")
     };
 
-    /**
-     * Find user by email. All users are stored in <code>private static final User[] users</code>
-     * @param email - the input parameter
-     * @return - user if his email is equal to passed email.
-     * Return <code>null</code> if there is no suitable user
-     */
-    public User findByEmail(String email) {
+    public User findByEmailClassic(String email) {
+        for (User user : users
+        ) {
+            if (user.getEmail().equals(email)) {
+                return user;
+            }
+        }
         return null;
     }
+
+    public Optional<User> findByEmail(String email) {
+        return Arrays.stream(users)
+                .filter(user -> user.getEmail().equals(email))
+                .findFirst();
+    }
+
 }