Android regular expression

Question

I have searched a lot for a regular expression or pattern that would work for me, but I haven't found any.

In a Edit text I want to allow first 4 digit and then 2 uppercase letters, so Ihave created a pattern:

private final Pattern sPattern  = Pattern.compile("^[0-9]{0,4}[A-Z]{0,2}");

But it allows first 2 capital letters, too.

If i change my pattern to

private final Pattern sPattern  = Pattern.compile("^[0-9]{0,4}[A-Z]{4,6}");

I am not able to get anything rright.

Please help me with this.

Thanks.

@Amee: {4,6} is a limiting quantifier that matches the preceding subpattern 4, 5 or 6 times. It has nothing to do with positions in string. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jul 8, 2015 at 10:44
@Amee Then you should probably get your hands on a regex tutorial or book, and start there. — Biffen
– Biffen, Commented Jul 8, 2015 at 10:51

Wiktor Stribiżew · Accepted Answer · 2015-07-08 10:52:23Z

1

You need to be careful with limiting quantifier. Just remove 0, as it allows less than 4 digits or 2 uppercase letters:

^[0-9]{4}[A-Z]{2}

This will require 4 digits at the beginning and 2 letters after.

See demo

For live validation, you can use

^[0-9]{0,4}(?:(?<=[0-9]{4})[A-Z]{0,2})?

It will allow a user to input 0 to 4 digits and then 0 to 2 English uppercase letters only if there are 4 digits before them. Mind that if the input can contain just these max 6 characters, you can add the $ end-of-string anchor at the end.

edited Jul 8, 2015 at 10:52

answered Jul 8, 2015 at 10:12

Wiktor Stribiżew

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18 Comments

Wiktor Stribiżew Over a year ago

Note that you cannot use 1 regex for both live input validation and final input validation. ^[0-9]{4}[A-Z]{2} is the regex to be used when the textbox loses focus (final validation). Your regex is quite fine for live validation, but you might want to check for at least 1 digit before a letter with ^[0-9]{1,4}[A-Z]{0,2}, or use a look-around to disallow only letters at the beginning: ^[0-9]{0,4}(?<=[0-9])[A-Z]{0,2}.

Amee Over a year ago

hello Stribizhev , This pattern allow me to add like 34AS also, I use this pattern ^[0-9]{0,4}(?<=[0-9])[A-Z]{0,2}

Wiktor Stribiżew Over a year ago

Sure it will. So, you want to use the regex for live validation, and the number of digits in the beginning must be exactly 4, right? And then a user should be able to type only 2 letters, right? Try ^[0-9]{0,4}(?:(?<=[0-9]{4})[A-Z]{0,2})?.

Amee Over a year ago

Thanks, it works now, Can u give any link or tutorial so that i can learn how to make regular expression???

Wiktor Stribiżew Over a year ago

You can learn a lot at regular-expressions.info, and use regexplanet or ocpsoft to quickly check simple regex patterns.

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