HashMap

public V put(K key, V value) {
        // 1. 初始化
        if (table == EMPTY_TABLE) {
            inflateTable(threshold);
        }
        // 2. 允许key为null的put
        if (key == null)
            return putForNullKey(value);
        // 3. 首先通过Hash计算Hash值，然后计算数组索引
        int hash = hash(key);
        int i = indexFor(hash, table.length);
        // 4. 处理冲突，遍历链表重新设置新值返回老值
        for (Entry<K,V> e = table[i]; e != null; e = e.next) {
            Object k;
            if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
                V oldValue = e.value;
                e.value = value;
                e.recordAccess(this);
                return oldValue;
            }
        }
        // 5. 无冲突，增加新值
        modCount++;
        addEntry(hash, key, value, i);
        return null;
    }

void addEntry(int hash, K key, V value, int bucketIndex) {
    // 1. 超过指定阀值进行扩容处理
    if ((size >= threshold) && (null != table[bucketIndex])) {
        resize(2 * table.length);
        hash = (null != key) ? hash(key) : 0;
        bucketIndex = indexFor(hash, table.length);
    }
    // 2. 创建数组对应的值
    createEntry(hash, key, value, bucketIndex);
}

void createEntry(int hash, K key, V value, int bucketIndex) {
    Entry<K,V> e = table[bucketIndex];
    table[bucketIndex] = new Entry<>(hash, key, value, e);
    size++;
}