Update User, Validator, and ValidationException classes

src/User.java

-package PACKAGE_NAME;
+public record User(String name, String email, String password) {
 
-public class User {
 }

src/ValidationException.java

-package PACKAGE_NAME;
+import java.util.List;
 
-public class ValidationException {
+public class ValidationException extends RuntimeException {
+    private final List<String> errors;
+
+    public ValidationException(List<String> errors) {
+        super("Validation failed with " + errors.size() + " error(s)");
+        this.errors = errors;
+    }
+
+    public List<String> getErrors() {
+        return errors;
+    }
 }

src/Validator.java

-package PACKAGE_NAME;
+import java.util.ArrayList;
+import java.util.List;
+
+    public class Validator<T> {
+        private final List<ValidationRule<T>> rules = new ArrayList<>();
+
+        public Validator<T> addRule(ValidationRule<T> rule) {
+            rules.add(rule);
+            return this;
+        }
+
+        public void validate(T object) {
+            List<String> errors = new ArrayList<>();
+            for (ValidationRule<T> rule : rules) {
+                String error = rule.validate(object);
+                if (error != null) {
+                    errors.add(error);
+                }
+            }
+
+            if (!errors.isEmpty()) {
+                throw new ValidationException(errors);
+            }
+        }
+    }
 
-public class Validator {
-}