FileStream in VB.net

I have some questions regarding the code below:

Dim sdirectory as string="C:\vb.net\files"
dim sfile as string="example.txt"
dim spath as string= sdirectory & sfile
dim sfilestrean as filestream
sfilestream=new filestream(spath,filemode.open,fileaccess.readwrite)


1-can I just use: dim spath as string="C:\vb.net\files\example.txt" instead of declaring Dim sdirectory as string="C:\vb.net\files"  then dim sfile as string="example.txt"?

2-when I put filemode.open, Fileaccess.write or Fileaccess.readwrite or Fileaccess.read or Fileaccess.none.   Does this mean if that file exists and accesseb by another user while this code is running can allow/prevent that user from read or write? please explain.


3- when I put filemode.createnew, Fileaccess.write or Fileaccess.readwrite or Fileaccess.read or Fileaccess.none.   Does this mean if that file exists and accesseb by another user while this code is running can allow/prevent that user from read or write? please explain.

Thanks