What is an openFileDescriptor mode?

Question

Why are there fileDescriptor modes (r,w,rw) and what are they for?

   contentResolver.openFileDescriptor(uri, "w")

They are described in the documention like this:

If opening with the exclusive "r" or "w" modes, the returned ParcelFileDescriptor could be a pipe or socket pair to enable streaming of data. Opening with the "rw" mode implies a file on disk that supports seeking. If possible, always use an exclusive mode to give the underlying ContentProvider the most flexibility.

Answer 1

These are nothing but modes in which you can open file descriptor.

• "r" Read only mode. cannot be used for writing
• "w" Write only mode. cannot be used for reading.
• "rw" for read-and-write.
• "rwt" for truncating or overwriting existing file contents.

(link to Android documentation)