Java: questions about radians, Math.cos, Math.sin, double and long

Question

I need to implement the harvesine distance in my java code.

I found this snippet in Javascript, and I need to convert it to java.

1. How can I convert latitude and longitude to radians in Java ?
2. Math.sin wants a double in Java. Should I pass the previously converted value in radians or not ?
3. Math.sin and Math.cos return long. Should I declare a as long and pass it to Math.sqrt or convert it to double ?

thanks

dLat = (lat2-lat1).toRad();
dLon = (lng2-lng1).toRad(); 
a = Math.sin(dLat/2) * Math.sin(dLat/2) +
    Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) * 
    Math.sin(dLon/2) * Math.sin(dLon/2); 
c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
d = R * c;
return d;

Answer 1

First of all, you should read the javadoc. sin(double) takes a double in parameter which is the angle in radians like said in the documentation. You'll also find on the linked page that sqrt takes a double as well.

Then, you should know that java can perform non-destructive conversion automatically. So if a method takes a double and you have a long, it will be no problem, since there's no loss in the conversion long -> double. The reverse is false, so Java refuse ton compile.

For the radians conversion, you'll find a toRadians method in the Math class.