在简单的数学计算中始终获得0值

Question

I'm testing an app that use this method

public double range(double[] myArray1, double[] myArray2, double[] myArray3) {
    int count=myArray1.length;

    double dfw = (3 * count) - 3;
    double msw = totalval / dfw;
    double critical = (2 / count) * (msw / 2);

    double range = Math.sqrt(critical);
    double crange = 3.95* range;

    return critical;
}

I have tried to print all values for an input of 3 arrays all with length 4;

dfw=9
msw=341.6388888888889
critical=0;
range=0;
crange=0;

All values are calculated correctly but when the execution reach critical , the values aren't calculated.

How is this thing possible? Why critical results always 0 causing a wrong output?

Answer 1

The problem is that (2 / count) is an Integer operation, which will return 0 if count > 2 .

To change it to a floating point operation, you can use a floating point literal, like this:

double critical = (2.0 / count) * (msw / 2);

Answer 2

you are performing integer math. int myvalue = 1/2 will give you myvalue = 0;

you can perform a cast

double critical = (2.0 / (double)count) * (msw / 2.0);

to promote count from int to double