/**
 * 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.
 * List實(shí)現(xiàn)所使用的標(biāo)記接口，用來(lái)表明實(shí)現(xiàn)了這些接口的list支持快速（通常是常數(shù)時(shí)間）隨機(jī)訪問(wèn)。
 * 這個(gè)接口的主要目的是允許一般的算法更改它們的行為，以便在隨機(jī)或者順序存取列表時(shí)能提供更好的性能。
 * <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.
 * 操作隨機(jī)訪問(wèn)列表（如ArrayList）的最佳算法在應(yīng)用于順序存取列表時(shí)，有可能產(chǎn)生二次項(xiàng)行為。
 * 泛型算法列表鼓勵(lì)在將某個(gè)算法應(yīng)用于順序存取列表可能導(dǎo)致差的性能之前，先檢查給定的列表是否是這個(gè)接口的一個(gè)實(shí)例，
 * 并在需要時(shí)去改變這些算法的行為以保證性能。
 * <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:

 * 隨機(jī)訪問(wèn)和順序存取之間的界限通常是模糊的。例如，一些List實(shí)現(xiàn)在變得很大時(shí)會(huì)導(dǎo)致漸進(jìn)的非線性訪問(wèn)時(shí)間，但實(shí)際上是常量訪問(wèn)時(shí)間。
 * 這樣的List實(shí)現(xiàn)通常都應(yīng)該實(shí)現(xiàn)該接口。
 * 一般來(lái)說(shuō)，某個(gè)List實(shí)現(xiàn)如果（對(duì)某些典型的類的實(shí)例來(lái)說(shuō)）滿足下面的條件，就應(yīng)該實(shí)現(xiàn)這個(gè)接口：循環(huán)
 * <pre>
 *   for (int i=0, n=list.size(); i &lt; n; i++)
 *     list.get(i);
 * </pre>
 * runs faster than this loop:
 * 比下面的循環(huán)運(yùn)行速度快。
 * <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" rel="external nofollow" >
 * Java Collections Framework</a>.
 * 這個(gè)接口是Java集合框架的一員。
 * @since 1.4
 */
public interface RandomAccess {
}

for (int i=0, n=list.size(); i < n; i++)
   list.get(i);

for (Iterator i=list.iterator(); i.hasNext(); )
   i.next();

 if (list instanceof RandomAccess)