Rounding a number up in Java

Question

I dont get how rounding numbers up to certain decimal places I looked everywhere tried every thing

currently I have my program to round up to a whole number with double rACT = Math.ceil(ACT); double rSAT = Math.ceil(SAT); double rGPA = Math.ceil(GPA);

but i need it to round up to 2 decimal places

FYI - I am an High school student I really dont need something super complicated to do this cuz I need my methods to be less then 15 I can waste any lines

http://stackoverflow.com/questions/153724/how-to-round-a-number-to-n-decimal-places-in-java — Vishal, Oct 28 '11 at 04:19
There is difference between rounding a number (to N-places) and obtaining a *string representation* with rounding/truncation rules applied... — , Oct 28 '11 at 04:27

Brendan Long · Answer 1 · 2011-10-28T17:33:31.037

11

There's probably a simpler way, but the obvious is:

double rSAT = Math.ceil(SAT * 100) / 100;

This turns a number like 2.123 into 212.3, rounds it to 213, then divides it back to 2.13.

edited Oct 28 '11 at 17:33

answered Oct 28 '11 at 04:18

Brendan Long

53,280
21
146
188

Actually, a call to `Math.ceil()` will round the number `212.3` to `213`. In math the ceiling function will round any number greater than a whole number to the next available whole number, so even `212.0003` would be rounded to `213`. You could use `Math.round()` which performs a standard rounding function and is equivalent to `Math.floor(decimal + 0.5)`. – Brandon Buck Oct 28 '11 at 17:16
@izuriel - The question specifies rounding numbers **up** (and they use `Math.ceil` too). Fixed my explanation though to say that it rounds 212.3 to 213. – Brendan Long Oct 28 '11 at 17:31
My take was that he was asking how to round a number and was giving the solution he was able to come up with. Either way, you specifically state that calling `Math.ceil()` on `212.3` will yield `212` which is incorrect, which was the main focus of my comment to inform you of that error. – Brandon Buck Oct 28 '11 at 17:34

score 2 · Answer 2 · answered Oct 28 '11 at 04:22

Usually, rounding is best done at the point of rendering the number (as a String, e.g.). That way the number can be stored/passed around with the highest precision and the information will only be truncated when displaying it to a user.

This code rounds to two decimal places at most and uses ceiling.

double unrounded = 3.21235;
NumberFormat fmt = NumberFormat.getNumberInstance();
fmt.setMaximumFractionDigits(2);
fmt.setRoundingMode(RoundingMode.CEILING);

String value = fmt.format(unrounded);
System.out.println(value);

score 0 · Answer 3 · edited May 23 '17 at 11:44

0

The question has been asked before, check out How to round a number to n decimal places in Java

the simplest solution, in my opinion, is this one, by chris:

double myNum = .912385;
int precision = 10000; //keep 4 digits
myNum= Math.floor(myNum * precision +.5)/precision;

edited May 23 '17 at 11:44

Community

1
1

answered Oct 28 '11 at 04:19

aleph_null

5,766
2
24
39

2

Why `Math.floor(x + 0.5)` instead of just `Math.ceil(x)`? – Brendan Long Oct 28 '11 at 04:20
adding 0.5 because, eg if number is 1.4 -> 1.4 + 0.5 = 1.9 , floor(1.9) = 1 if number is 1.6 -> 1.6+0.5 = 2.1 floor(2.1) = 2 so rounding up working this way – Zohaib Oct 28 '11 at 04:38
Might as well just round up using the function designed for it (`Math.ceil`). – Brendan Long Oct 28 '11 at 04:58

score 0 · Answer 4 · answered Oct 28 '11 at 04:30

0

If you are looking for a string representation of a number you can do like below:

DecimalFormat df = new DecimalFormat("#.00");
System.out.println(df.format(12.912385));

answered Oct 28 '11 at 04:30

Vishal

19,879
23
80
93

Rounding a number up in Java

4 Answers4