/**
 * Marker interface used by List 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實現(xiàn)所使用的標記接口，用來表明實現(xiàn)了這些接口的list支持快速（通常是常數(shù)時間）隨機訪問。
 * 這個接口的主要目的是允許一般的算法更改它們的行為，以便在隨機或者順序存取列表時能提供更好的性能。
 * 
The best algorithms for manipulating random access lists (such as
 * ArrayList) can produce quadratic behavior when applied to
 * sequential access lists (such as LinkedList). Generic list
 * algorithms are encouraged to check whether the given list is an
 * instanceof 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.
 * 操作隨機訪問列表（如ArrayList）的最佳算法在應(yīng)用于順序存取列表時，有可能產(chǎn)生二次項行為。
 * 泛型算法列表鼓勵在將某個算法應(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接口的一個實例，
 * 并在需要時去改變這些算法的行為以保證性能。
 * 
It is recognized that the distinction between random and sequential
 * access is often fuzzy. For example, some List implementations
 * provide asymptotically linear access times if they get huge, but constant
 * access times in practice. Such a List implementation
 * should generally implement this interface. As a rule of thumb, a
 * List implementation should implement this interface if,
 * for typical instances of the class, this loop:

 * 隨機訪問和順序存取之間的界限通常是模糊的。例如，一些List實現(xiàn)在變得很大時會導(dǎo)致漸進的非線性訪問時間，但實際上是常量訪問時間。
 * 這樣的List實現(xiàn)通常都應(yīng)該實現(xiàn)該接口。
 * 一般來說，某個List實現(xiàn)如果（對某些典型的類的實例來說）滿足下面的條件，就應(yīng)該實現(xiàn)這個接口：循環(huán)
 * 
 *   for (int i=0, n=list.size(); i < n; i++)
 *     list.get(i);
 * 
 * runs faster than this loop:
 * 比下面的循環(huán)運行速度快。
 * 
 *   for (Iterator i=list.iterator(); i.hasNext(); )
 *     i.next();
 * 
 *
 * 
This interface is a member of the
 * 
 * Java Collections Framework.
 * 這個接口是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)