MY HASHMAP

README.md → src/README.md

@@ -8,4 +8,4 @@ Be attentive to basic requirements for the implementation of the map (initial ca
 
 P.S.: you can implement other methods of the Map interface.
 
-[Try to avoid these common mistakes while solving task](./checklist.md)
+[Try to avoid these common mistakes while solving task](../checklist.md)

src/test/java/core/basesyntax/MyHashMap.java

@@ -0,0 +1,95 @@
+package core.basesyntax;
+
+import java.util.Objects;
+public class MyHashMap<K, V> implements MyMap<K, V> {
+    private static final int DEFAULT_CAPACITY = 16;
+    private static final float DEFAULT_LOAD_FACTOR = 0.75f;
+    private static final int RESIZE_MULTIPLIER = 2;
+    private Node<K, V>[] table;
+    private int size;
+    private int threshold;
+
+    public MyHashMap() {
+        table = new Node[DEFAULT_CAPACITY];
+        threshold = (int) (DEFAULT_CAPACITY * DEFAULT_LOAD_FACTOR);
+    }
+
+    @Override
+    public void put(K key, V value) {
+        if (size >= threshold) {
+            resize();
+        }
+        int index = getIndex(key, table.length);
+        Node<K, V> current = table[index];
+        if (current == null) {
+            table[index] = new Node<>(key, value, null);
+            size++;
+            return;
+        }
+        Node<K, V> prev = null;
+        while (current != null) {
+            if (Objects.equals(current.key, key)) {
+                current.value = value;
+                return;
+            }
+            prev = current;
+            current = current.next;
+        }
+        prev.next = new Node<>(key, value, null);
+        size++;
+    }
+
+    @Override
+    public V getValue(K key) {
+        int index = getIndex(key, table.length);
+        Node<K, V> current = table[index];
+        while (current != null) {
+            if (Objects.equals(current.key, key)) {
+                return current.value;
+            }
+            current = current.next;
+        }
+        return null;
+    }
+
+    @Override
+    public int getSize() {
+        return size;
+    }
+
+    private void resize() {
+        Node<K, V>[] oldTable = table;
+        int newCapacity = oldTable.length * RESIZE_MULTIPLIER;
+        table = new Node[newCapacity];
+        threshold = (int) (newCapacity * DEFAULT_LOAD_FACTOR);
+        size = 0;
+        for (Node<K, V> headNode : oldTable) {
+            while (headNode != null) {
+                Node<K, V> nextNode = headNode.next;
+                int index = getIndex(headNode.key, newCapacity);
+                headNode.next = table[index];
+                table[index] = headNode;
+                size++;
+                headNode = nextNode;
+            }
+        }
+    }
+
+    private int getIndex(K key, int length) {
+        if (key == null) {
+            return 0;
+        }
+        return (key.hashCode() & 0x7fffffff) % length;
+    }
+
+    private static class Node<K, V> {
+        private final K key;
+        private V value;
+        private Node<K, V> next;
+        Node(K key, V value, Node<K, V> next) {
+            this.key = key;
+            this.value = value;
+            this.next = next;
+        }
+    }
+}

src/test/java/core/basesyntax/MyMap.java

@@ -0,0 +1,7 @@
+package core.basesyntax;
+
+public interface MyMap<K, V> {
+    void put(K key, V value);
+    V getValue(K key);
+    int getSize();
+}