说明：  苹果电脑公司（Apple Computer, Inc.）为用户提供了全套免费的Cocoa程序开发工具，这套工具 就是我们所说的Xcode。它随着Mac OSX一起发行，当然，你也可以在苹果公司的网站下载。
(Apple Computer Inc. (Apple Computer, Inc.) Provides users with a full set free Cocoa application development tools, this tool What we call Xcode. It is issued in conjunction with Mac OSX, of course, you can also download at Apple s Web site.)