I have the following error codes:
Those are not "error codes". They are part
of a Java stacktrace.
If we can see the entire stacktrace, then it
may be possible to figure out what it means.
However, the lines you have included provided
nothing that can (realistically) be used for
You added this:
Conversion = '-'
This is telling us that somewhere in your code
you are directly or indirectly using a
Format (or similar) to generate or
parse a string. It would appear that the format
string is incorrect.
My guess is that this is happening in your
showStudents() method, but without a
complete stacktrace (and the code of that method)
it is not possible to be sure.