When you create a new Expression in report layout you can do some arithmetic operations with your columns.
Let's say we have three number columns C1, C2, C3 with integer values and our expression is
E = (C1 - C2) / C3
In this case the result will be an integer. For example (6-2)/3 = 1
If we want a double result of the expression we have to tell that at least one term of the fraction is of double type.
The expression language accepts java methods for corresponding objects. So we have to write:
E = (C1 - C2) / C3.doubleValue()
In this case (6-2)/3 = 1,33333..
