Main.java

public class Main<K, V> {
    private static final int CAPACITY = 16;
    private Entry<K, V>[] table;
    private int size;

    static class Entry<K, V> {
        K key;
        V value;
        Entry<K, V> next;

        Entry(K key, V value) {
            this.key = key;
            this.value = value;
        }
    }

    @SuppressWarnings("unchecked")
    public Main() {
        table = new Entry[CAPACITY];
        size = 0;
    }

    private int hash(K key) {
        if (key == null) return 0;
        return Math.abs(key.hashCode() % table.length);
    }

    public void put(K key, V value) {
        int index = hash(key);
        Entry<K, V> entry = table[index];

        while (entry != null) {
            if ((key == null && entry.key == null) ||
                    (key != null && key.equals(entry.key))) {
                entry.value = value;
                return;
            }
            entry = entry.next;
        }

        Entry<K, V> newEntry = new Entry<>(key, value);
        newEntry.next = table[index];
        table[index] = newEntry;
        size++;
    }

    public V get(K key) {
        int index = hash(key);
        Entry<K, V> entry = table[index];

        while (entry != null) {
            if ((key == null && entry.key == null) ||
                    (key != null && key.equals(entry.key))) {
                return entry.value;
            }
            entry = entry.next;
        }

        return null;
    }

    public V remove(K key) {
        int index = hash(key);
        Entry<K, V> entry = table[index];
        Entry<K, V> prev = null;

        while (entry != null) {
            if ((key == null && entry.key == null) ||
                    (key != null && key.equals(entry.key))) {
                if (prev == null) {
                    table[index] = entry.next;
                } else {
                    prev.next = entry.next;
                }
                size--;
                return entry.value;
            }
            prev = entry;
            entry = entry.next;
        }

        return null;
    }
}