Java regex on doubles

Question

I'm trying to check for a double that has a maximum of 13 digits before the decimal point and the decimal point and numbers following it are optional. So the user could write a whole number or a number with decimals.

To start with I had this:

if (check.matches("[0-9](.[0-9]*)?"))

I've been through several pages on Google and haven't had any luck getting it working despite various efforts. My thought was to do it like this but it doesn't work:

[0-9]{1,13}(.[0-9]*)?

How can I do it?

Why don't you just parse the `double` and check for `value < 10000000000000`? — Alvin Wong, Jan 28 '13 at 13:32

score 14 · Accepted Answer · answered Jan 28 '13 at 13:30

14

Don't forget to escape the dot.

if (check.matches("[0-9]{1,13}(\\.[0-9]*)?"))

answered Jan 28 '13 at 13:30

John Kugelman

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Perfect thank you. I tried something similar but I was a bit naive to try use a regex checker online which can't accept "\\". Should have just tried it in the program. – Duane Jan 28 '13 at 13:37

score 5 · Answer 2 · answered Jan 28 '13 at 13:32

5

First of all you need to escape the dot(in java this would be [0-9]{1,13}(\\.[0-9]*)?). Second of all don't forget there is also another popular representation of doubles - scientific. So this 1.5e+4 is again a valid double number. And lastly don't forget a double number may be negative, or may not have a whole part at all. E.g. -1.3 and .56 are valid doubles.

answered Jan 28 '13 at 13:32

Ivaylo Strandjev

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It's for an accounting system exercise where we can't have negative numbers. – Duane Jan 28 '13 at 13:38
Any solution that handles all these cases ? – Rahul Feb 23 '21 at 16:42

score 2 · Answer 3 · answered Jan 28 '13 at 13:31

2

You need to escape the dot and you need at least on digit after the dot

[0-9]{1,13}(\\.[0-9]+)?

See it here on Regexr

answered Jan 28 '13 at 13:31

stema

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score 1 · Answer 4 · answered Dec 28 '14 at 05:32

1

John's answer is close. But a '-' needs to be added, in case it's negative, if you accept negative values. So, it would be modified to -?[0-9]{1,13}(\.[0-9]*)?

answered Dec 28 '14 at 05:32

Trenton D. Adams

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score 1 · Answer 5 · answered Feb 17 '15 at 13:52

1

if you need to validate decimal with commas and negatives:

Object testObject = "-1.5";
boolean isDecimal = Pattern.matches("^[\\+\\-]{0,1}[0-9]+[\\.\\,]{1}[0-9]+$", (CharSequence) testObject);

Good luck.

answered Feb 17 '15 at 13:52

august0490

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score 0 · Answer 6 · answered Jul 09 '20 at 13:07

You can use \d+(\.\d*)? as below in kotlin language-

    val rawString = "Hi..  2345.97 ..Bye"
    val DOUBLE_PATTERN = Pattern.compile("\\d+(\\.\\d*)?")
    val matcher = DOUBLE_PATTERN.matcher(rawString)
    var filterNumber = 0.0
    if (matcher.find())
        filterNumber = matcher.group() // extracted number- 2345.97

Java regex on doubles

6 Answers6

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