It uses the idea of Seive of Eratosthenes.
The code is basically does the following to find Prime Numbers :
1) Populate Array from 0 - > MAX
2) Find 1st Prime, which is 2
3) Delete all Multiple of 2, i.e set it to false
4) Find next prime, which is 3
5) Delete all multiple of 3
6) Repeat steps 4 - 6 until done.
I also use a little try and catch, just to provide as an example.