复制文件的程序。命令格式如下：java copy 源文件名 目标文件名。

该程序将源文件复制到目标文件，然后显示这个文件中的字节数。如果源文件不存在，就会告知用户找不到这个文件。如果目标文件已经存在，就告知用户目标文件存在。

-Copy the files. Command format is as follows: java copy source file name destination file name. The program will copy the source file to the target file, and then displays the number of bytes in the file. If the source file does not exist, it will inform the user can not find the file. If the target file already exists, inform the user of the target file exists.