Java Regular Expression to match dollar amounts

Question

This is what i've been using

\$?[0-9]+\.*[0-9]*

But when i was doing some testing i noticed that things like

$$$34.00

would return as a match (but matcher.group()) just returns the matched substring. I don't want it to even pass the regular expression if the user enters more than one dollar sign so i tried this:

\${1}[0-9]+\.*[0-9]*

but this seems to behave the same as the regular expression i first typed. Right now i'm testing this in java but, i plan to use it in c++ using the Boost libraries. But Please don't give me that solution here because i'm trying to learn without someone giving me the answer.

But i do need help making it so the user can only enter one dollar sign (which is what i thought \${1} would do)

you can specify the begin and end of a string like ^\${1}[0-9]+\.*[0-9]*$ — Eric.K.Yung, Jul 25 '13 at 17:03
Is the amount the whole string? Also, how do you match it currently? Using `.find()`? — fge, Jul 25 '13 at 17:05
@Eric.K.Yung looks like ^\$?[0-9]+\.*[0-9]*$ does what i want. I want the user to be able to enter a dollar amount with a dollar sign or w/o a dollar sign — rage, Jul 25 '13 at 17:12
I know this is an old question but this website REALLY helped me understand RegEx https://regexr.com — brandito, Mar 16 '18 at 02:38

score 19 · Answer 1 · answered Jul 25 '13 at 18:30

19

I would suggest avoiding the use of regular expressions for currency parsing, esp when Java provides you much simpler ways to solve this problem.

Consider this code:

String str = "$789.11"; // user entered value
Number number = null;
try {
    number = NumberFormat.getCurrencyInstance(Locale.US).parse(str);
} catch(ParseException pe) {
    // ignore
}

if (number != null) {
   // proceed as user entered a good value
}
else {
   // user didn't enter a good value
}

answered Jul 25 '13 at 18:30

anubhava

664,788
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2

shame I can't +1 this more times – sjr Jul 25 '13 at 18:37
1

This is pretty neat and i will definitely store it away in my toolbox but, I am trying to learn regular expressions so that was why i was trying to find a solution to this problem. – rage Jul 25 '13 at 18:46
Yes sure, its your prerogative. However just to let you know currency string can contain comma as well e.g. `$23,456.78` – anubhava Jul 25 '13 at 18:48
@rage: Check this answer for some pointers about using regex to parse US currency string: http://stackoverflow.com/questions/354044/what-is-the-best-u-s-currency-regex – anubhava Jul 25 '13 at 18:52
1

The `.parse(str)` method accepts incorrect strings like `$12asdf`. – Dean Schulze Dec 05 '17 at 19:20
I agree with Dean. I don't think the main response is +1. – ozn Oct 08 '18 at 05:58

Syon · Accepted Answer · 2013-07-25T20:06:03.093

12

Since you're doing this to learn regex...

^\$(([1-9]\d{0,2}(,\d{3})*)|(([1-9]\d*)?\d))(\.\d\d)?$

Breakdown:

^\$ start of string with $ a single dollar sign

([1-9]\d{0,2}(,\d{3})*) 1-3 digits where the first digit is not a 0, followed by 0 or more occurrences of a comma with 3 digits

or

(([1-9]\d*)?\d) 1 or more digits where the first digit can be 0 only if it's the only digit

(\.\d\d)?$ with a period and 2 digits optionally at the end of the string

Matches:

$4,098.09
$4098.09
$0.35
$0
$380

Does not match:

$098.09
$0.9
$10,98.09
$10,980456

edited Jul 25 '13 at 20:06

answered Jul 25 '13 at 19:27

Syon

6,625
5
33
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`(([1-9]\d*)?\d)` also takes care if the user does not enter commas doesn't it? I'm glad you posted this answer because i really learned alot from breaking up that regex myself and understanding it piece by piece – rage Jul 25 '13 at 19:56
Yes, that portion is specifically to capture when no commas are used in the string. – Syon Jul 25 '13 at 19:58
What is the opposite to get the $amount alone – Ashok kumar Ganesan May 27 '20 at 09:27

Song Gao · Answer 3 · 2013-07-25T17:59:59.690

2

You can do something like [^\$]*\$? in the beginning. This would insure that there are no duplicate $ signs, but also matches if there is no $ present.

Also, if you are working with currency (possible decimal and 2 digits after), you should use [\.\d{2}]?.

This says that it can be a match if it's followed by ONE instance of a period and 2 digits or nothing at all. As stated in the comments, it can also match multiple periods in a row, so you shouldn't use the * quantifier after \.

edited Jul 25 '13 at 17:59

answered Jul 25 '13 at 17:54

Song Gao

656
4
14

I didn't want to force the user into adding cents if he didn't need to. . would `\.{0,1}` work for that? – rage Jul 25 '13 at 18:10
`\.?` is the same as `\.{0,1}`.The `?` quantifier means it happens either once or not at all. You should also include the two possible cent digits after the period as I showed in my answer. Without them, `$27.50` would only match `$27.` – Song Gao Jul 25 '13 at 18:31

score 1 · Answer 4 · answered Jul 25 '13 at 17:00

1

You are missing ^(beginning of string),$(end of string)

^\$\d+([.][0-9]+)?$

answered Jul 25 '13 at 17:00

Anirudha

30,881
7
64
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score 0 · Answer 5 · answered Nov 13 '15 at 07:08

0

i know this is coming late but this seems to work for me

(\$)?[0-9]+\.*[0-9]*

i dont understand why it didnt work for you.

answered Nov 13 '15 at 07:08

nightcrawler1020

1

Zaven Zareyan · Answer 6 · 2016-03-13T08:41:45.997

-1

[$](([1-9]+\.?\d*)|([0]\.\d*)|[0]) pattern ideally for this case.

This is standard Perl regex but could be use in JAVA with some libs.

edited Mar 13 '16 at 08:41

answered Mar 12 '16 at 20:27

Zaven Zareyan

1,360
8
15

Java Regular Expression to match dollar amounts

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