I'm sure your motives were great, but we don't like people to post ready-made solutions here - particularly in the 'Beginners' forum.
It's much better to guide someone to their own solution. Please read the NotACodeMill (←click) page.
I've kept your original post, and if my colleagues ask me to, I'll restore it.
so you pass in 3 numbers assign them to variables with very bad names a,b,c so we have no idea what you intended to do with them, you then do nothing with them.
the controlling loop in countPrimes always goes from 2 to MAX_PRIME.
this is just a nice layout thing...
you do not need to indent the validation try catch blocks within each other
Joined: Oct 13, 2005
This sounds like a project Euler question. Is it?
I would suggest you create an array and use a sieve of Eratosthenes to work out whether each number is prime. Then count the primes. 0 and 1 don’t count. Much more effecient than an isPrime method.