created simplified custom array-list by 3xactCoder · Pull Request #1742 · mate-academy/jv-array-list

3xactCoder · 2026-02-06T14:26:26Z

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mateacademy-ai-mentor

Review Summary

Great work on your ArrayList implementation! You've correctly handled most of the core logic, including capacity management, index checks, and using System.arraycopy for element shifting. However, this requires changes because the use of Arrays.copyOf() is not allowed for this task, as it violates a key requirement [CHECKLIST ITEM #2]. The goal is to implement this functionality yourself. To fix this, please replace Arrays.copyOf() in your resizing method. You should manually create a new array with the calculated new size and then use System.arraycopy() to copy the elements from the old array into the new one. Once you've made that change, your solution will be in great shape!

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mateacademy-ai-mentor · 2026-02-06T14:27:46Z

src/main/java/core/basesyntax/ArrayList.java

@@ -1,48 +1,103 @@
 package core.basesyntax;

+import java.util.Arrays;


This violates checklist item #2: 'Don't use Objects, Arrays, or any other util class.' This import should be removed, and the functionality from this class should be implemented manually.

mateacademy-ai-mentor · 2026-02-06T14:27:46Z

src/main/java/core/basesyntax/ArrayList.java

+    public void checkCapacity() {
+        if (count == elements.length) {
+            int newSize = elements.length + elements.length / 2;
+            elements = Arrays.copyOf(elements,newSize);


This violates checklist item #2: 'Don't use Objects, Arrays, or any other util class.' Instead of using Arrays.copyOf(), you should create a new array of newSize and then use System.arraycopy() to copy the elements from the old elements array to the new one.

mateacademy-ai-mentor

Review Summary

Great job on the progress so far, especially with replacing Arrays.copyOf! Your solution is very close. However, changes are needed to fix two remaining issues.

First, the addAll method will cause an infinite loop if a list is added to itself (e.g., myList.addAll(myList)). This is because the loop condition list.size() is re-evaluated after each add operation, which increases the size. A good way to solve this is to copy the elements from the incoming collection into a separate array before you start adding them.

Second, the array growth logic in your checkCapacity method uses the magic number 2. Please extract this into a named constant to comply with the checklist requirement [CHECKLIST ITEM #3].

After you fix these two points, your solution will be in great shape!

✨ 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.

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mateacademy-ai-mentor · 2026-02-06T14:42:37Z

src/main/java/core/basesyntax/ArrayList.java

    @Override
    public void addAll(List<T> list) {
-
+        for (int i = 0;i < list.size();i++) {


The current implementation of addAll will cause an infinite loop if the list is added to itself (e.g., myList.addAll(myList)). This is because list.size() is re-evaluated on each loop iteration, but add() increases the size of the list. To meet the requirement that your implementation behaves like java.util.ArrayList, this case needs to be handled correctly.

mateacademy-ai-mentor · 2026-02-06T14:42:37Z

src/main/java/core/basesyntax/ArrayList.java

+
+    public void checkCapacity() {
+        if (count == elements.length) {
+            int newSize = elements.length + elements.length / 2;


This line uses the magic number 2 for the growth calculation. This violates checklist item #3: 'Any magic numbers should be constants'. Please extract this value into a named constant, for example GROWTH_DIVISOR, to improve readability and maintainability.

mateacademy-ai-mentor

Review Summary

Excellent work on the fixes! I am approving this solution as an educational override to help you move forward, but please review the following points for your next tasks. You did a great job fixing the addAll method and extracting the magic number.

Here are a few areas for improvement:

Naming: The constant MAGIC_NUM is not very descriptive. A name like GROWTH_RATE_DIVISOR would better explain its purpose. [CHECKLIST ITEM #6]
Encapsulation: Helper methods like checkIndex and checkCapacity should be private to hide the internal implementation details of the class.
Growth Logic: There's a subtle bug in the growth calculation. If the array size is 1, 1 + 1 / 2 results in 1 due to integer division, which prevents the array from growing. The new size must always be at least current size + 1.

These are common refinements in programming. Keep up the great effort!

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mateacademy-ai-mentor · 2026-02-06T14:51:54Z

src/main/java/core/basesyntax/ArrayList.java

+
 public class ArrayList<T> implements List<T> {
+    private static final int DEFAULT_SIZE = 10;
+    private static final int MAGIC_NUM = 2;


This is a great improvement to extract the magic number 2. However, MAGIC_NUM is not a very informative name. According to checklist item #6 ('Use informative names for your variables and methods'), a name should make it clear what the variable is responsible for. A name like GROWTH_RATE_DIVISOR or CAPACITY_GROWTH_DIVIDER would better describe its purpose in the capacity calculation.

mateacademy-ai-mentor · 2026-02-06T14:51:54Z

src/main/java/core/basesyntax/ArrayList.java

+    public void checkIndex(int index) {
+        if (index < 0 || index >= count) {
+            throw new ArrayListIndexOutOfBoundsException("Index is incorrect");
+        }
+    }
+
+    public void checkCapacity() {


These helper methods (checkIndex and checkCapacity) are part of the internal implementation of your ArrayList. To properly encapsulate the class's logic and prevent them from being called from outside the class, they should be declared as private.

mateacademy-ai-mentor · 2026-02-06T14:51:54Z

src/main/java/core/basesyntax/ArrayList.java

+        }
+    }
+
+    public void checkCapacity() {


The checklist (item #6) provides a good example regarding method names that contain conditional logic. Since this method only grows the array if it's full, a more descriptive name would be growIfFull() or ensureCapacityIsSufficient(). This makes it clearer to the reader what the method does.

mateacademy-ai-mentor · 2026-02-06T14:51:54Z

src/main/java/core/basesyntax/ArrayList.java

+
+    public void checkCapacity() {
+        if (count == elements.length) {
+            int newSize = elements.length + elements.length / MAGIC_NUM;


There's a subtle issue with this growth calculation for small array sizes. If elements.length is 1, newSize will also be 1 due to integer division (1 + 1 / 2 = 1 + 0 = 1). This means the array won't grow, which will lead to an ArrayIndexOutOfBoundsException on the next add operation. The new size must always be at least current size + 1.

created simplified custom array-list

9489e67

mateacademy-ai-mentor suggested changes Feb 6, 2026

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3xactCoder added 2 commits February 6, 2026 16:32

created simplified custom array-list(fixed)

c83b09a

created simplified custom array-list(fix)

9757414

3xactCoder requested a review from mateacademy-ai-mentor February 6, 2026 14:40

mateacademy-ai-mentor suggested changes Feb 6, 2026

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created simplified custom array-list(fix2)

958fdec

3xactCoder requested a review from mateacademy-ai-mentor February 6, 2026 14:49

mateacademy-ai-mentor approved these changes Feb 6, 2026

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created simplified custom array-list#1742

created simplified custom array-list#1742
3xactCoder wants to merge 4 commits intomate-academy:masterfrom
3xactCoder:array-list-task

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		@@ -1,48 +1,103 @@
		package core.basesyntax;

		import java.util.Arrays;

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3xactCoder commented Feb 6, 2026

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