I have these two variables
double num = 540.512
double sum = 1978.8
Then I did this expression
double total = Math.round((num/ sum * 100) * 10) / 10;
but I end up with 27.0.
In fact I have many other variables and when I use them in the expression I always get a 0 in the tenth's place.
If you need this and similar operations more often, it may be more convenient to find the right library instead of implementing it yourself.
Here are one-liners solving your question from Apache Commons Math using Precision, Colt using Functions, and Weka using Utils:
double value = 540.512 / 1978.8 * 100;
// Apache commons math
double rounded1 = Precision.round(value, 1);
double rounded2 = Precision.round(value, 1, BigDecimal.ROUND_HALF_UP);
// Colt
double rounded3 = Functions.round(0.1).apply(value)
// Weka
double rounded4 = Utils.roundDouble(value, 1)
Maven dependencies:
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-math3</artifactId>
<version>3.5</version>
</dependency>
<dependency>
<groupId>colt</groupId>
<artifactId>colt</artifactId>
<version>1.2.0</version>
</dependency>
<dependency>
<groupId>nz.ac.waikato.cms.weka</groupId>
<artifactId>weka-stable</artifactId>
<version>3.6.12</version>
</dependency>
The Math.round
method returns a long
(or an int
if you pass in a float
), and Java's integer division is the culprit. Cast it back to a double
, or use a double
literal when dividing by 10
. Either:
double total = (double) Math.round((num / sum * 100) * 10) / 10;
or
double total = Math.round((num / sum * 100) * 10) / 10.0;
Then you should get
27.3
Helpful method I created a while ago...
private static double round (double value, int precision) {
int scale = (int) Math.pow(10, precision);
return (double) Math.round(value * scale) / scale;
}
Double toBeTruncated = new Double("2.25");
Double truncatedDouble = new BigDecimal(toBeTruncated).setScale(1, BigDecimal.ROUND_HALF_UP).doubleValue();
it will return 2.3
Your method is right, all you have to do is add a .0 after both the tens and it will fix your problem!
double example = Math.round((187/35) * 10.0) / 10.0;
The output would be:
5.3
DecimalFormat decimalFormat = new DecimalFormat(".#");
String result = decimalFormat.format(12.763); // --> 12.7
A neat alternative that is much more readable in my opinion, however, arguably a tad less efficient due to the conversions between double and String:
double num = 540.512;
double sum = 1978.8;
// NOTE: This does take care of rounding
String str = String.format("%.1f", (num/sum) * 100.0);
If you want the answer as a double, you could of course convert it back:
double ans = Double.parseDouble(str);
Double number = new Double("5.25");
Double tDouble =
new BigDecimal(number).setScale(1, BigDecimal.ROUND_HALF_UP).doubleValue();
this will return it will return 5.3
try this
for example
DecimalFormat df = new DecimalFormat("#.##");
df.format(55.544545);
output:
55.54
Source: Stackoverflow.com