feat(DEVELOP): create hashMap #1598

Gosyav · 2025-09-16T12:44:18Z

No description provided.

mateacademy-ai-mentor

Review Summary

I’m requesting changes because there is a critical correctness bug that can cause runtime failures, plus a couple of checklist violations to address.

Critical blocker (must fix to pass):

Negative bucket index due to Math.abs(hash) when hash == Integer.MIN_VALUE (lines: put ~33, getValue ~67, resize rehash ~95). This can produce a negative index and lead to ArrayIndexOutOfBoundsException. Fix by computing a non-negative index, e.g. int idx = (hash & 0x7fffffff) % capacity; (or bit-mask if capacity is a power of two). Apply consistently in put/getValue/resize.

Other required checklist fixes:

Private members order: the private inner Node class is declared before public API (lines 10–19). Move Node to the end of the class (after public methods) to comply with “private after public”.
Encapsulation: resize() is declared public (around line 88) but is an internal helper. Change it to private and keep it after public methods.

Minor improvements (nice to have):

Replace magic literal 2 in capacity growth (line ~89 table.length * 2) with a constant, e.g. private static final int RESIZE_MULTIPLIER = 2;.
Remove leading/redundant blank lines (top of file line 2 and any extra empty lines inside methods) per checklist.

Your core logic (chaining, updates, null key/value handling, resize flow) is solid. Address the index calculation and checklist items above and you should be in great shape. Keep going!

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

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mateacademy-ai-mentor · 2025-09-16T12:52:17Z

src/main/java/core/basesyntax/MyHashMap.java

+    private static class Node<K, V> {
+        private final K key;
+        private V value;
+        private Node<K, V> next;
+
+        public Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
+    }


This violates checklist item: "Private methods and classes should be after public ones in your class." The private inner Node class is declared at the top of the class (lines 10–19). Move the Node class to after the public methods (for example, at the end of the class) so private helpers follow the public API. See checklist guidance: .

mateacademy-ai-mentor · 2025-09-16T12:52:17Z

src/main/java/core/basesyntax/MyHashMap.java

+    public void resize() {
+        int newCapacity = table.length * 2;
+
+        Node<K, V>[] newTable = new Node[newCapacity];
+
+        for (Node<K, V> node : table) {
+            while (node != null) {
+                int newIndex = node.key == null ? 0 : Math.abs(node.key.hashCode()) % newCapacity;
+                Node<K, V> nextNode = node.next;
+
+                node.next = newTable[newIndex];
+                newTable[newIndex] = node;
+                node = nextNode;
+            }
+        }
+
+        table = newTable;
+        threshold = (int) (newCapacity * LOAD_FACTOR);
    }


This violates checklist item: "If the method has only a utility purpose and is used only inside the same class, it should not be public. Keep your code as close as possible to follow the encapsulation principle." The resize() method is declared public (line 88) but is an internal helper used only by this class. Change its visibility to private and keep it after public methods. See checklist guidance: .

mateacademy-ai-mentor · 2025-09-16T12:52:17Z

src/main/java/core/basesyntax/MyHashMap.java

+    }
+
+    public void resize() {
+        int newCapacity = table.length * 2;


This violates checklist item: "Any magic numbers should be constants". The resize multiplier is used as a literal at line 89 (table.length * 2). Introduce a named constant such as private static final int RESIZE_MULTIPLIER = 2; and use it to compute the new capacity so numeric intent is explicit. See checklist guidance: .

mateacademy-ai-mentor · 2025-09-16T12:52:17Z

src/main/java/core/basesyntax/MyHashMap.java

+        int index = key == null ? 0 : Math.abs(key.hashCode()) % table.length;
+        Node<K, V> newNode = new Node<>(key, value);

+        if (table[index] == null) {
+            table[index] = newNode;
+            size++;
+            return;
+        }
+
+        Node<K, V> currentNode = table[index];
+
+        while (true) {
+            if ((currentNode.key == null && key == null)
+                    || (currentNode.key != null && currentNode.key.equals(key))) {
+                currentNode.value = value;
+                return;
+            }
+
+            if (currentNode.next == null) {
+                currentNode.next = newNode;
+                size++;
+                return;
+            }
+
+            currentNode = currentNode.next;
+        }
    }

    @Override
    public V getValue(K key) {
+        if (table == null) {
+            return null;
+        }
+
+        int index = key == null ? 0 : Math.abs(key.hashCode()) % table.length;
+
+        Node<K, V> currentNode = table[index];
+
+        while (currentNode != null) {
+            if ((currentNode.key == null && key == null)
+                    || (currentNode.key != null && currentNode.key.equals(key))) {
+                return currentNode.value;
+            }
+
+            currentNode = currentNode.next;
+        }
+
        return null;
    }

    @Override
    public int getSize() {
-        return 0;
+        return size;
+    }
+
+    public void resize() {
+        int newCapacity = table.length * 2;
+
+        Node<K, V>[] newTable = new Node[newCapacity];
+
+        for (Node<K, V> node : table) {
+            while (node != null) {
+                int newIndex = node.key == null ? 0 : Math.abs(node.key.hashCode()) % newCapacity;


Correctness issue (must fix): computing bucket index with Math.abs(key.hashCode()) % capacity can yield a negative index when hashCode() equals Integer.MIN_VALUE. This pattern appears in put (line 33), getValue (line 67), and resize rehashing (line 95). Replace with a safe computation such as (key.hashCode() & 0x7fffffff) % capacity or use masking when capacity is a power of two. Without this change, the code can throw ArrayIndexOutOfBoundsException at runtime.

mateacademy-ai-mentor · 2025-09-16T12:52:17Z

src/main/java/core/basesyntax/MyHashMap.java

@@ -1,19 +1,107 @@
 package core.basesyntax;



This violates checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)" There is a leading redundant empty line at the top of the file (line 2) and several redundant blank lines inside the class. Remove leading and unnecessary blank lines at method/class starts to comply with the style checklist. See checklist guidance: .

mateacademy-ai-mentor

Review Summary

Decision: Approve. Functionality and requirements are met; only minor style issues remain.

Your MyHashMap correctly implements put, getValue, and getSize, handles updates without increasing size, manages collisions via chaining, and resizes/rehashes properly. The non-negative index computation resolves the previous critical bug.
The remaining issues are stylistic: there are several redundant empty lines (e.g., at the top of the class, between fields, before local logic in put, inside the put loop, around getValue index calculation, inside getValue, before resize, and inside resize). These violate the checklist rule to avoid starting class/method bodies with blank lines and to remove redundant empty lines. Please remove those blanks to fully comply.
Optional polish: consider adding a brief comment explaining the bitmask in getIndex and, if desired, a localized @SuppressWarnings("unchecked") around new Node[...] array creation.

Nice work on correctness and structure—just tidy the extra blank lines to align with the checklist.

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

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mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+    private static final int DEFAULT_CAPACITY = 16;
+    private static final float LOAD_FACTOR = 0.75f;
+    private static final int RESIZE_MULTIPLIER = 2;
+


Redundant empty line. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Please remove the empty line at the top of the class to match the checklist.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+    private int threshold;
+    private int size;
+    private Node<K, V>[] table;
+


Redundant empty line. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Please remove this extra blank line between fields.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+        if (size >= threshold) {
+            resize();
+        }
+


Redundant empty line before local logic. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Delete the unnecessary blank line.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+
+        int index = getIndex(key, table.length);
+        Node<K, V> newNode = new Node<>(key, value);
+


Redundant empty line. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Remove it to keep the file compact.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+                currentNode.value = value;
+                return;
+            }
+


Redundant empty line inside put loop area. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Please remove.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+                size++;
+                return;
+            }
+


Redundant empty line. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Remove this blank line.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+        if (table == null) {
+            return null;
+        }
+


Redundant empty line before index calculation in getValue. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Please remove.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+
+        int index = getIndex(key, table.length);
+        Node<K, V> currentNode = table[index];
+


Redundant empty line inside getValue. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Remove the extra blank line for consistency.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

-        return 0;
+        return size;
+    }
+


Redundant empty line before the resize method. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Please remove.

mateacademy-ai-mentor · 2025-09-16T13:24:42Z

src/main/java/core/basesyntax/MyHashMap.java

+    private void resize() {
+        int newCapacity = table.length * RESIZE_MULTIPLIER;
+        Node<K, V>[] newTable = new Node[newCapacity];
+


Redundant empty line inside resize logic. This violates the checklist item: "Don't begin class or method implementation with empty line. Remove all redundant empty lines, be careful :)". Remove it to satisfy the checklist.

feat(DEVELOP): create hashMap

ca1ca92

mateacademy-ai-mentor suggested changes Sep 16, 2025

View reviewed changes

fix(DEVELOP): fix

adc2d60

Gosyav requested a review from mateacademy-ai-mentor September 16, 2025 13:19

mateacademy-ai-mentor approved these changes Sep 16, 2025

View reviewed changes


		int index = getIndex(key, table.length);
		Node<K, V> newNode = new Node<>(key, value);


		int index = getIndex(key, table.length);
		Node<K, V> currentNode = table[index];

feat(DEVELOP): create hashMap #1598

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