Implementation of MyMap interface

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

@@ -1,19 +1,100 @@
 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 double LOAD_FACTOR = 0.75;
+    private int size;
+    private int capacity;
+    private int threshold;
+    private Node<K, V>[] buckets;
+
+    public MyHashMap() {
+        capacity = DEFAULT_CAPACITY;
+        threshold = (int) (LOAD_FACTOR * capacity);
+        buckets = (Node<K, V>[]) new Node[capacity];
+    }
 
     @Override
     public void put(K key, V value) {
+        checkSize();
+        Node<K, V> newNode = new Node<>(key, value);
+        int index = getIndex(key);
+        insertNode(newNode, index);
 
     }
 
     @Override
     public V getValue(K key) {
-        return null;
+        int index = getIndex(key);
+        Node<K, V> bucket = buckets[index];
+        while (bucket != null && !Objects.equals(bucket.key, key)) {
+            bucket = bucket.next;
+        }
+        return bucket != null ? bucket.value : null;
     }
 
     @Override
     public int getSize() {
-        return 0;
+        return size;
+    }
+
+    private void checkSize() {
+        if (size >= threshold) {
+            resize();
+        }
+    }
+
+    private void resize() {
+        capacity *= 2;
+        threshold = (int) (LOAD_FACTOR * capacity);
+        size = 0;
+        Node<K, V>[] oldCopy = buckets;
+        buckets = (Node<K, V>[]) new Node[capacity];
+        for (Node<K, V> node : oldCopy) {
+            while (node != null) {
+                Node<K, V> next = node.next;
+                node.next = null;
+                insertNode(node, getIndex(node.key));
+                node = next;
+            }
+        }
+    }
+
+    private int getIndex(K key) {
+        return (key == null) ? 0 : (key.hashCode() & Integer.MAX_VALUE) % capacity;
+    }
+
+    private void insertNode(Node<K, V> newNode, int index) {
+        Node<K, V> bucket = buckets[index];
+        if (bucket == null) {
+            newNode.next = bucket;
+            buckets[index] = newNode;
+            size++;
+        } else if (Objects.equals(bucket.key, newNode.key)) {
+            bucket.value = newNode.value;
+        } else {
+            while (bucket.next != null) {
+                if (Objects.equals(bucket.key, newNode.key)) {
+                    bucket.value = newNode.value;
+                    return;
+                }
+                bucket = bucket.next;
+            }
+            bucket.next = newNode;
+            size++;
+        }
+    }
+
+    private static class Node<K, V> {
+        private final K key;
+        private V value;
+        private Node<K, V> next;
+
+        Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
     }
 }