设计一合并文本文件程序，可按以下步骤实现：l　　创建一窗口框架；l　　输入三个文本文件名（可用FileDialog对象进行文件选择）；l　　分别打开前面两个文件，将其内容合并到第三个文件上，也就是file3 = file1 + file2。l　　然后再将file3的内容显示在窗口上。-Design a text file merging procedures, according to the following steps: l to create a window frame　L three text input file name (FileDialog object is created for file selection available)　L respectively open the front two files, merge the content to the third document, namely file3 = file1 and file2. L then file3 content displayed in the window.