说明： 编写一个JAVA Application程序，包括一个“打开”按钮和一个TextArea，用户点击按钮时将弹出FileDialog，请用户选择一个文本文件，然后关闭FileDialog，程序把这个文本文件的内容显示在TextArea中。 (prepared a JAVA Application procedures including an "open" button and a TextArea. when users click on the button will pop FileDialog, users choose a text file, FileDialog then closed, the procedure, the text revealed the contents of the documents were in TextArea.)
