Calculations with floating numbers

Question

I am doing some calculations within an application have have found the following happens:
System.out.println("calculation: " + (22.0*4.4));
results in the output:
calculation: 96.80000000000001
Why is this? I understand that rounding has to happen on sum figures, but not these two - how can I get the 'proper' result of 96.8??
Thanks

Answer 1

import java.math.BigDecimal;
public class Test {
    public static void main(String[] args) {
        double d1 = 22.0;
        double d2 = 4.4;
        System.out.println(d1);
        System.out.println(d2);
        // with Java 5.0 printf
        System.out.printf("%.1f%n", d1 * d2);
        // With BigDecimal
        BigDecimal bd1 = new BigDecimal(d1);
        BigDecimal bd2 = new BigDecimal(d2);
        System.out.println(bd1);
        System.out.println(bd2);
        BigDecimal product = bd1.multiply(bd2);
        BigDecimal scaled = product.setScale(1, BigDecimal.ROUND_HALF_UP);
        System.out.println(scaled);
}Cheers, Neil