Convert string to decimal number with 2 decimal places in Java

Question

In Java, I am trying to parse a string of format "###.##" to a float. The string should always have 2 decimal places.

Even if the String has value 123.00, the float should also be 123.00, not 123.0.

This is what I have so far:

System.out.println("string liters of petrol putting in preferences is " + stringLitersOfPetrol);

Float litersOfPetrol = Float.parseFloat(stringLitersOfPetrol);

DecimalFormat df = new DecimalFormat("0.00");
df.setMaximumFractionDigits(2);

litersOfPetrol = Float.parseFloat(df.format(litersOfPetrol));

System.out.println("liters of petrol before putting in editor: " + litersOfPetrol);

It prints:

string liters of petrol putting in preferences is 010.00 
liters of petrol before putting in editor: 10.0

That can't be done using float and double. BigDecimal can do that. — Bhesh Gurung, Jul 04 '13 at 07:55
if it is not possible to do using float or double, is there any other way to retain 2 decimal places with which the incoming string is coming? — adityag, Jul 04 '13 at 07:58
It _is_ possible as many answers suggest: just use `BigDecimal`. — fge, Jul 04 '13 at 08:17
possible duplicate of [How to round a number to n decimal places in Java](http://stackoverflow.com/questions/153724/how-to-round-a-number-to-n-decimal-places-in-java) — user207421, Jul 04 '13 at 10:36

score 19 · Accepted Answer · edited Oct 03 '13 at 17:52

This line is your problem:

litersOfPetrol = Float.parseFloat(df.format(litersOfPetrol));

There you formatted your float to string as you wanted, but but then that string got transformed again to a float, and then what you printed in stdout was your float that got a standard formatting. Take a look at this code

import java.text.DecimalFormat;

String stringLitersOfPetrol = "123.00";
System.out.println("string liters of petrol putting in preferences is "+stringLitersOfPetrol);
Float litersOfPetrol=Float.parseFloat(stringLitersOfPetrol);
DecimalFormat df = new DecimalFormat("0.00");
df.setMaximumFractionDigits(2);
stringLitersOfPetrol = df.format(litersOfPetrol);
System.out.println("liters of petrol before putting in editor : "+stringLitersOfPetrol);

And by the way, when you want to use decimals, forget the existence of double and float as others suggested and just use BigDecimal object, it will save you a lot of headache.

Thanks ! I got it ! And now I am using java.lang.BigDecimal instead of float — adityag, Jul 04 '13 at 11:09

score 18 · Answer 2 · answered Jan 05 '14 at 21:05

Java convert a String to decimal:

String dennis = "0.00000008880000";
double f = Double.parseDouble(dennis);
System.out.println(f);
System.out.println(String.format("%.7f", f));
System.out.println(String.format("%.9f", new BigDecimal(f)));
System.out.println(String.format("%.35f", new BigDecimal(f)));
System.out.println(String.format("%.2f", new BigDecimal(f)));

This prints:

8.88E-8
0.0000001
0.000000089
0.00000008880000000000000106383001366
0.00

score 8 · Answer 3 · answered Jul 04 '13 at 07:56

8

Use BigDecimal:

new BigDecimal(theInputString);

It retains all decimal digits. And you are sure of the exact representation since it uses decimal base, not binary base, to store the precision/scale/etc.

And it is not subject to precision loss like float or double are, unless you explicitly ask it to.

answered Jul 04 '13 at 07:56

fge

119,121
33
254
329

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I doubt that with two decimal places, precision loss is an issue – Cephalopod Jul 04 '13 at 07:59
I know, but if you deal only with two decimal places, this will never be a problem. Even Intels are not that inaccurate. – Cephalopod Jul 04 '13 at 08:11
1

@Arian even with "only" two decimal places, as you say, this is a problem. Since IEEE 754 does NOT talk in decimal to begin with, but in binary. – fge Jul 04 '13 at 08:17
Why Double.parsedouble("2.30") returns 2.3? and not 2.30? – Aman Verma Feb 19 '19 at 18:30

score 3 · Answer 4 · answered Jul 04 '13 at 10:22

I just want to be sure that the float number will also have 2 decimal places after converting that string.

You can't, because floating point numbers don't have decimal places. They have binary places, which aren't commensurate with decimal places.

If you want decimal places, use a decimal radix.

score 2 · Answer 5 · answered Jul 04 '13 at 07:58

2

litersOfPetrol = Float.parseFloat(df.format(litersOfPetrol));

System.out.println("liters of petrol before putting in editor : "+litersOfPetrol);

You print Float here, that has no format at all.

To print formatted float, just use

String formatted = df.format(litersOfPetrol);
System.out.println("liters of petrol before putting in editor : " + formatted);

answered Jul 04 '13 at 07:58

GKlimov

409
2
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Why Double.parsedouble("2.30") returns 2.3? and not 2.30? – Aman Verma Feb 19 '19 at 18:30

AllTooSir · Answer 6 · 2013-07-04T08:01:13.587

Float.parseFloat() is the problem as it returns a new float.

Returns a new float initialized to the value represented by the specified String, as performed by the valueOf method of class Float.

You are formatting just for the purpose of display . It doesn't mean the float will be represented by the same format internally .

You can use java.lang.BigDecimal.

I am not sure why are you using parseFloat() twice. If you want to display the float in a certain format then just format it and display it.

Float litersOfPetrol=Float.parseFloat(stringLitersOfPetrol);
DecimalFormat df = new DecimalFormat("0.00");
df.setMaximumFractionDigits(2);
System.out.println("liters of petrol before putting in editor"+df.format(litersOfPetrol));

Convert string to decimal number with 2 decimal places in Java

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