RandomAccess

• List實現了該接口,說明該實現類的數據可以進行隨機訪問,不需要保證順序性.比如ArrayList實現了該接口,LinkedList沒有實現該接口.
• 隨機訪問列表使用循環遍歷，順序訪問列表使用迭代器遍歷。

JDK定義

/**
 * 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.
 *
 * <p>The best algorithms for manipulating random access lists (such as
 * <tt>ArrayList</tt>) can produce quadratic behavior when applied to
 * sequential access lists (such as <tt>LinkedList</tt>).  Generic list
 * algorithms are encouraged to check whether the given list is an
 * <tt>instanceof</tt> this interface before applying an algorithm that would
 * provide poor performance if it were applied to a sequential access list,
 * and to alter their behavior if necessary to guarantee acceptable
 * performance.
 *
 * <p>It is recognized that the distinction between random and sequential
 * access is often fuzzy.  For example, some <tt>List</tt> implementations
 * provide asymptotically linear access times if they get huge, but constant
 * access times in practice.  Such a <tt>List</tt> implementation
 * should generally implement this interface.  As a rule of thumb, a
 * <tt>List</tt> implementation should implement this interface if,
 * for typical instances of the class, this loop:
 * <pre>
 *     for (int i=0, n=list.size(); i &lt; n; i++)
 *         list.get(i);
 * </pre>
 * runs faster than this loop:
 * <pre>
 *     for (Iterator i=list.iterator(); i.hasNext(); )
 *         i.next();
 * </pre>
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.4
 */

• List的實現類使用的標記接口,一般來標識該實現類能夠支持快速隨機訪問.
• 接口存在的目的:繼承該接口的實現類,能夠允許一般的算法來更改他們的行為,yibian在隨機或者循環訪問列表時,能夠提供更好的性能.
• 對于隨機訪問的列表(ArrayList)的操作方法應用到順序訪問的列表(LinkedList),將會產生二次項行為(個人理解應該是額外的操作吧).所以,對不同訪問類型的列表,我們需要采用最為合適的算法.
• 總結來講,隨機訪問類型的列表進行loop遍歷的時間更短,順序訪問類型的列表通過Iterator進行遍歷的時間更短.
  參考文章:RandomAccess 接口使用