first commit

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

@@ -1,19 +1,87 @@
 package core.basesyntax;
 
 public class MyHashMap<K, V> implements MyMap<K, V> {
+    private Node<K, V>[] table;
+    private int size;
+    private static final int DEFAULT_CAPACITY = 16;
+    private static final float LOAD_FACTOR = 0.75f;
+
+
+    public MyHashMap() {
+        table = new Node[DEFAULT_CAPACITY];
+        size = 0;
+    }
+
+    private void checkThreshold() {
+        if (size >= table.length * LOAD_FACTOR) {
+            resize();
+        }
+    }
+
+    private void resize() {
+        Node<K, V>[] oldTable = table;
+        table = new Node[oldTable.length * 2];
+        size = 0;
+
+        for (Node<K, V> node : oldTable) {
+            while (node != null) {
+                put(node.key, node.value);
+                node = node.next;
+            }
+        }
+    }
 
     @Override
     public void put(K key, V value) {
+        int hash = key == null ? 0 : key.hashCode();
+        int index = hash & (table.length - 1);
+
+        Node<K, V> current = table[index];
+        while (current != null) {
+            if ((current.key == null && key == null) || (current.key != null && current.key.equals(key))) {
+                current.value = value;
+                return;
+            }
+            current = current.next;
+        }
 
+        Node<K, V> newNode = new Node<>(key, value);
+        newNode.hash = hash;
+        newNode.next = table[index];
+        table[index] = newNode;
+        size++;
+        checkThreshold();
     }
 
     @Override
     public V getValue(K key) {
+        int hash = key == null ? 0 : key.hashCode();
+        int index = hash & (table.length - 1);
+
+        Node<K, V> current = table[index];
+        while (current != null) {
+            if ((current.key == null && key == null) || (current.key != null && current.key.equals(key))) {
+                return current.value;
+            }
+            current = current.next;
+        }
         return null;
     }
 
     @Override
     public int getSize() {
-        return 0;
+        return size;
+    }
+
+    private static class Node<K, V> {
+        private final K key;
+        private V value;
+        private int hash;
+        private Node<K, V> next;
+
+        public Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
     }
 }