Mohammad Ashrafuddin Ferdousi wrote:... and think that, this is build on GWT.
Yes, it is made in GWT, I am glad you liked it.
however I believe its not heavy weight..
It is true that as your application gets larger and larger the server side compiling takes longer time, but the client does not increase in size
Please search about generating random numbers. You will find several threads from last week. This is a discussion about a similar problem, which I believe you will find helpful. You will see there are at least two ways to get random numbers in a range, and you will also find a pitfall mentioned.