这这这没有因果关系啊：实现了 RandomAccess 接口，因此支持随机访问。
而且应该是 快速随机访问。
Marker interface used by <tt>List</tt> implementations to indicate that
* they support fast (generally constant time) random access. The primary
* purpose of this interface is to allow generic algorithms to alter their
* behavior to provide good performance when applied to either random or
* sequential access lists.
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