a.
The default value for object variables is null, so curLine will be null and the while loop will never get executed.

b.
When the BufferedReader reaches the end of the file, it indicates this by returning null.  The loop will work properly, but the last time through the loop, curLine will be null, so your program will print out "null" at the end.

c.
We've restructured the loop to use a do-while loop, but it still will have the same problem as example b.