RandomAccess接口

package java.util;
// * 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.
//空接口，标记接口，支持快速随机访问,ArrayList实现了此接口
public interface RandomAccess {
}