Regex check if a string contains only digits doesn't work

Question

This is my code and I have no idea why it returns false

    "A123".matches("\\D+");

Jens · Accepted Answer · 2015-03-18 10:48:58Z

3

it must be:

"A123".matches("^\\d+$");

lowercase d stands for a digit ^ for the beginning of the string and ^ for the end of the string.

answered Mar 18, 2015 at 10:48

Jens

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fge Over a year ago

No need for anchors; look at my answer

fge · Accepted Answer · 2015-03-18 10:50:07Z

1

It is because you are yet another victim among the tens/hundreds of Java devs who are bitten daily by the fact that .matches() is misnamed.

It will try and match the whole input. This is not what you want.

You have to go through a Pattern, a Matcher and .find() instead:

private static final Pattern NONDIGIT = Pattern.compile("\\D");

// Test whether there is any nondigit character in a string:
NONDIGIT.matcher(theString).find();

You should especially do that since anyway .matches() will recompile a Pattern each time; here, you have only one Pattern.

answered Mar 18, 2015 at 10:50

fge

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Comments

Rahul Tripathi · Accepted Answer · 2015-03-18 10:56:56Z

1

You can try this:

"A123".matches("[0-9]+")

Also as you have tagged it as Java then there is an alternate way to use NumberUtil.isNumber(String str) from Apache which can check this for you.

edited Mar 18, 2015 at 10:56

answered Mar 18, 2015 at 10:51

Rahul Tripathi

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