google提供的完整说明：
public abstract MenuItemsetShortcut(char numericChar, char alphaChar)
Since: API Level 1
Change both the numeric and alphabetic shortcut associated with this item. Note that the shortcut will be triggered when the key that generates the given character is pressed alone or along with with the alt key. Also note that case is not significant and that alphabetic shortcut characters will be displayed in lower case.
See Menu for the menu types that support shortcuts.
Parameters
numericChar The numeric shortcut key. This is the shortcut when using a numeric (e.g., 12-key) keyboard.
alphaChar The alphabetic shortcut key. This is the shortcut when using a keyboard with alphabetic keys.
ReturnsThis Item so additional setters can be called.
也查了网上的资料，的确两个参数都是快捷键。
你可以使用setShortcut方法给菜单项指定快捷键。每一次调用setShortcut需要两个快捷键，一个是数字键，另一个可以是全键盘中的键。任何键不区分大小写。
下面的代码片段给出了如何为两种模式设定快捷键：
// Add a shortcut to this menu item, ‘0’ if using the numeric keypad
// or ‘b’ if using the full keyboard.
menuItem.setShortcut(‘0’, ‘b’);
但是为什么只有字母快捷键起效，就不知道了。
