Question

I don’t understand why are float values different from double values. From the example bellow it appears that float provides different result than double for the same operation:

public class Test {

    public static void main(String[] args) {
        double a = 99999.8d;
        double b = 99999.65d;
        System.out.println(a + b);

        float a2 = 99999.8f;
        float b2 = 99999.65f;
        System.out.println(a2 + b2);
    }
}

Output:

199999.45
199999.44

Can you explain what makes this difference between float and double?

Answer 1

A float is a 32 bit IEEE 754 floating point.

A double is a 64 bit IEEE 754 floating point.

so it is just a matter of precision because neither of the fraction portions .8 and .65 have a terminating binary representation, so there is some rounding error. the double has more precision so it has slightly less rounding error.

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html