HashMap-查找源码

public V get(Object key) {
    Node<K,V> e;
    // 同样需要经过扰动函数计算哈希值
    return (e = getNode(hash(key), key)) == null ? null : e.value;
}

final Node<K,V> getNode(int hash, Object key) {
    Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
    // 判断桶数组的是否为空和长度值
    if ((tab = table) != null && (n = tab.length) > 0 &&
        // 计算下标，哈希值与数组长度-1
        (first = tab[(n - 1) & hash]) != null) {
        if (first.hash == hash && // always check first node
            ((k = first.key) == key || (key != null && key.equals(k))))
            return first;
        if ((e = first.next) != null) {
            // TreeNode 节点直接调用红黑树的查找方法，时间复杂度O(logn)
            if (first instanceof TreeNode)
                return ((TreeNode<K,V>)first).getTreeNode(hash, key);
            // 如果是链表就依次遍历查找
            do {
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    return e;
            } while ((e = e.next) != null);
        }
    }
    return null;
}