Answer 1

This class is the general class of exceptions produced by failed or interrupted I/O operations

Most of the time Java throws IOException when :

Reading a network file and got disconnected.
Reading a local file that was no longer available.
Using some stream to read data and some other process closed the stream.
Trying to read/write a file but don't have permission.
Trying to write to a file but disk space was no longer available.

https://stackoverflow.com/questions/13216148/java-what-throws-an-ioexception