Big problem often because of little problem

Today, when I try to doing my data mining assignment, I meet a wrong result in my program. However, I try to find the problem in many ways but nothing.

In final, I find it: In java, integer divide integer always got a integer. If you make a mistake like I do, the result is always zero. Because the dividend is less than divisor.

Mistake is the biggest problem to a programming learner like me. So be careful when program.