数据传输功能，选择、粘贴和复制相应数据。包括的主要的类有：清除、粘贴板、选择、复制和粘贴-Copyright (c) 2000 David Flanagan. All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd Edition. * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.