private static int inputCommand(){

int command;

try {

command = input.nextInt();

return command;

} catch (Exception e) {

//若输入字符型或者字符串，则抛出异常，捕获该异常，抛出”错误命令异常“

   input = new Scanner(System.in);

//返回-1

return -1;

}

}

}

其中 input = new Scanner(System.in);有什么用？