Java translation(author inactive)

Returning values of different data types is a bad design.

Calculating the product of integers in range (a; b) is the same as calculating the product of integers in range [a; b].

a=58 b=60  
✘  Expected: 58.99999999999998, instead got: 59  

This should be an issue.

And another problem is I always failed at the big number

  a=21 b=47  
✘  Expected: 1.0770249922811275e+38, instead got: 1.0770249922811271e+38  

For some range of numbers (e.g. [9,26]), there is a rounding issue that makes my code fail.

Expected: 42744736671436790000, instead got: 42744736671436800000

Here's part of my solution:

for (var i=a+1, res=1; i < b; i++){
  res *= i;
}