Jv dependency injection by Volodymyr8787 · Pull Request #1262 · mate-academy/jv-dependency-injection

Volodymyr8787 · 2026-07-17T18:24:03Z

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mateacademy-ai-mentor

Review Summary

The Injector implementation has several critical functional issues and violates explicit checklist requirements that will cause test failures. First, the createNewImstance method lacks the required @Component annotation check (clazz.isAnnotationPresent(Component.class)) before instantiation — this is explicitly mandated by checklist item #4. Second, the loop at line 36 creates a new instance for EACH @Inject field instead of creating ONE instance and injecting all fields into it, breaking singleton behavior. Third, the interfaceImplementations map is populated inside findImplementation() on every call rather than being initialized once as a class field using Map.of() (checklist item #6). Fourth, the catch block uses multiple specific exceptions (NoSuchMethodException | InstantiationException | IllegalAccessException | InvocationTargetException) instead of their common parent ReflectiveOperationException (checklist item #8), and caught exceptions are not chained to the RuntimeException (checklist item #7). Checkstyle violations are noted but are non-blocking since the build compiles successfully — focus on fixing the functional issues first.

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mateacademy-ai-mentor · 2026-07-17T18:26:31Z

+        }
+        return clazzImplementationInstance;
+    }
+


Checklist item #4 violated: There's no check for @Component annotation before creating an instance. According to the task requirements, if the Component annotation is missing above the class, we shouldn't be able to create an instance and should throw an exception. The createNewImstance method should verify clazz.isAnnotationPresent(Component.class) before instantiation.

mateacademy-ai-mentor · 2026-07-17T18:26:31Z

 public class Injector {
    private static final Injector injector = new Injector();
+    private Map<Class<?>, Object> instances = new HashMap<>();
+    Map<Class<?>, Class<?>> interfaceImplementations = new HashMap<>();


Checklist item #6 violated: The interfaceImplementations map should be filled using Map.of() instead of new HashMap<>(). Change line 20 to: Map<Class<?>, Class<?>> interfaceImplementations = Map.of(...) and initialize it with all three mappings.

mateacademy-ai-mentor · 2026-07-17T18:26:31Z

+            return instance;
+        } catch (NoSuchMethodException | InstantiationException
+                 | IllegalAccessException | InvocationTargetException e) {


Checklist item #8 violated: Lines 64-66 catch multiple specific exceptions. According to checklist, it is better to replace many exceptions that have a common parent with a general parental exception. Use catch (ReflectiveOperationException e) instead, as all these exceptions (NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException) inherit from it.

mateacademy-ai-mentor · 2026-07-17T18:26:31Z

+    private Class<?> findImplementation(Class<?> interfaceClazz) {
+        interfaceImplementations.put(FileReaderService.class, FileReaderServiceImpl.class);
+        interfaceImplementations.put(ProductParser.class, ProductParserImpl.class);


Lines 72-74 populate the map on every call to findImplementation. This should be done once during initialization, not repeatedly. Move this initialization to a constructor or static initializer block, or initialize the map directly at declaration using Map.of().

mateacademy-ai-mentor · 2026-07-17T18:26:31Z

+    @Inject
    private FileReaderService fileReaderService;

    @Override


Checklist item #6 violation: interfaceImplementations should be initialized using Map.of() as a class field, not populated with put() inside findImplementation(). Change line 20 to: Map<Class, Class> interfaceImplementations = Map.of(FileReaderService.class, FileReaderServiceImpl.class, ProductParser.class, ProductParserImpl.class, ProductService.class, ProductServiceImpl.class);

mateacademy-ai-mentor

Review Summary

The Injector.java implementation has four critical violations of mandatory checklist requirements that must be fixed before approval. First, the @Component annotation check at line 27 happens AFTER instantiation at line 26 - it must be moved to createNewInstance() or before calling it per [CHECKLIST ITEM #4]. Second, the interfaceImplementations map at line 17 is a HashMap populated with put() calls inside findImplementation() on every invocation instead of using Map.of() as a one-time class field initializer [CHECKLIST ITEM #6]. Third, both catch blocks in createNewInstance() don't chain exceptions - use throw new RuntimeException("message", e) instead of just throw new RuntimeException("message") [CHECKLIST ITEM #7]. Fourth, replace multiple specific exceptions (NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException) with their common parent ReflectiveOperationException [CHECKLIST ITEM #8]. The service implementation classes are correctly done - focus on fixing the Injector class.

✨ Please rate this review in the Platform's notification center¹. I will be grateful for your feedback! ✨

Important

Fix the issues, commit the changes, and then re-request my review using the Re-request review button² in the Reviewers tab.

Tip

If you have any comments about this review, please leave a message in the Add a comment section below and mention me with the @mateacademy-ai-mentor tag³.
I will read your message during my next review of your pull request. Please do not reply directly to my comments, as that feature is not supported yet.

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mateacademy-ai-mentor · 2026-07-17T18:56:07Z

+    }
+
+    private Class<?> findImplementation(Class<?> interfaceClazz) {
+        interfaceImplementations.put(FileReaderService.class, FileReaderServiceImpl.class);


This violates checklist item #6: The interface implementations map should be initialized using Map.of() as a class field initializer, not populated with put() calls inside the method on every invocation. Move these mappings to line 17.

mateacademy-ai-mentor · 2026-07-17T18:56:07Z

-        return null;
+        Class<?> clazz = findImplementation(interfaceClazz);
+        Object clazzImplementationInstance = createNewInstance(clazz);
+        if (!clazz.isAnnotationPresent(Component.class)) {


The @Component check happens AFTER createNewInstance() is called at line 26. This violates checklist item #4 - the check must happen BEFORE instantiation. Move this validation to createNewInstance() or before calling it.

mateacademy-ai-mentor · 2026-07-17T18:56:07Z

+                    fields.setAccessible(true);
+                    fields.set(clazzImplementationInstance, fieldsInstance);
+                } catch (IllegalAccessException e) {
+                    throw new RuntimeException("Can't initialize field value."


This violates checklist item #7: The caught exception is not chained to the RuntimeException. Use the constructor's second parameter: throw new RuntimeException(..., e);

mateacademy-ai-mentor · 2026-07-17T18:56:07Z

+            return instance;
+        } catch (NoSuchMethodException | InstantiationException


This violates checklist item #8: Replace multiple specific exceptions (NoSuchMethodException | InstantiationException | IllegalAccessException | InvocationTargetException) with their common parent ReflectiveOperationException.

mateacademy-ai-mentor · 2026-07-17T18:56:07Z

+            return instance;
+        } catch (NoSuchMethodException | InstantiationException
+                 | IllegalAccessException | InvocationTargetException e) {
+            throw new RuntimeException("Can't create a new instance of " + clazz.getName());


This violates checklist item #7: The caught exception is not chained to the RuntimeException. Add the caught exception as the second parameter to the RuntimeException constructor.

mateacademy-ai-mentor · 2026-07-17T18:56:07Z

+        interfaceImplementations.put(FileReaderService.class, FileReaderServiceImpl.class);
+        interfaceImplementations.put(ProductParser.class, ProductParserImpl.class);
+        interfaceImplementations.put(ProductService.class, ProductServiceImpl.class);


Checklist item #5 violation: The interfaceImplementations.put() calls at lines 69-71 should not be inside this method. Move map initialization to a field initializer using Map.of() at declaration time (line 17).

mateacademy-ai-mentor

Review Summary

This is an educational override to help you continue learning. Your Injector.java implementation shows solid progress — the @component validation, interfaceImplementations map with Map.of(), and ReflectiveOperationException on line 62 are all correct. Two remaining items to fix before the next level: 1) Add exception chaining on line 46 by changing throw new RuntimeException("Can't initialize field value...") to throw new RuntimeException("Can't initialize field value. Class: " + clazz.getName() + ". Field: " + fields.getName(), e) per [CHECKLIST ITEM #7]; 2) Replace IllegalAccessException with ReflectiveOperationException on line 42 to be consistent with line 62 per [CHECKLIST ITEM #8]. You're almost there — these are quick fixes that will make your error handling much more maintainable. Keep going!

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mateacademy-ai-mentor · 2026-07-17T19:34:30Z

+                    fields.set(clazzImplementationInstance, fieldsInstance);
+                } catch (IllegalAccessException e) {
+                    throw new RuntimeException("Can't initialize field value."
+                            + "Class: " + clazz.getName() + ". Field: "


CHECKLIST ITEM #7 VIOLATION: The exception is not chained to the RuntimeException. Use throw new RuntimeException("message", e) to include the caught exception.

mateacademy-ai-mentor · 2026-07-17T19:34:30Z

+
+                try {
+                    fields.setAccessible(true);
+                    fields.set(clazzImplementationInstance, fieldsInstance);


CHECKLIST ITEM #8 VIOLATION: Replace IllegalAccessException with ReflectiveOperationException which is its parent class (consistent with line 62).

Volodymyr8787 added 2 commits July 17, 2026 20:23

created and annotated

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complete task

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mateacademy-ai-mentor suggested changes Jul 17, 2026

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fixes mistakes

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Volodymyr8787 requested a review from mateacademy-ai-mentor July 17, 2026 18:54

mateacademy-ai-mentor suggested changes Jul 17, 2026

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fix

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Volodymyr8787 requested a review from mateacademy-ai-mentor July 17, 2026 19:32

mateacademy-ai-mentor approved these changes Jul 17, 2026

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		return instance;
		} catch (NoSuchMethodException \| InstantiationException

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