Finding substring in RegEx Java

Question

Hello I have a question about RegEx. I am currently trying to find a way to grab a substring of any letter followed by any two numbers such as: d09.

I came up with the RegEx ^[a-z]{1}[0-9]{2}$ and ran it on the string

sedfdhajkldsfakdsakvsdfasdfr30.reed.op.1xp0

However, it never finds r30, the code below shows my approach in Java.

Pattern pattern = Pattern.compile("^[a-z]{1}[0-9]{2}$");
Matcher matcher = pattern.matcher("sedfdhajkldsfakdsakvsdfasdfr30.reed.op.1xp0");

if(matcher.matches())
    System.out.println(matcher.group(1));

it never prints out anything because matcher never finds the substring (when I run it through the debugger), what am I doing wrong?

Mark Byers · Accepted Answer · 2012-12-25 01:44:22Z

6

There are three errors:

Your expression contains anchors. ^ matches only at the start of the string, and $ only matches at the end. So your regular expression will match "r30" but not "foo_r30_bar". You are searching for a substring so you should remove the anchors.
The matches should be find.
You don't have a group 1 because you have no parentheses in your regular expression. Use group() instead of group(1).

Try this:

Pattern pattern = Pattern.compile("[a-z][0-9]{2}");
Matcher matcher = pattern.matcher("sedfdhajkldsfakdsakvsdfasdfr30.reed.op.1xp0");

if(matcher.find()) {
    System.out.println(matcher.group());    
}

ideone

Matcher Documentation

A matcher is created from a pattern by invoking the pattern's matcher method. Once created, a matcher can be used to perform three different kinds of match operations:

The matches method attempts to match the entire input sequence against the pattern.

The lookingAt method attempts to match the input sequence, starting at the beginning, against the pattern.

The find method scans the input sequence looking for the next subsequence that matches the pattern.

edited Dec 25, 2012 at 1:44

answered Dec 25, 2012 at 1:32

Mark Byers

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1 Comment

HerrPfister Over a year ago

Worked like a charm. Thank you I really appreciate it!

Javier Diaz · Accepted Answer · 2012-12-25 01:33:19Z

2

It doesn't match because ^ and $ delimite the start and the end of the string. If you want it to be anywhere, remove that and you will succed.

answered Dec 25, 2012 at 1:33

Javier Diaz

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Comments

fge · Accepted Answer · 2012-12-25 01:33:28Z

1

Your regex is anchored, as such it will never match unless the whole input matches your regex. Use [a-z][0-9]{2}.
Don't use .matches() but .find(): .matches() is shamefully misnamed and tries to match the whole input.

answered Dec 25, 2012 at 1:33

fge

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Comments

hologram · Accepted Answer · 2012-12-25 01:41:34Z

0

How about "[a-z][0-9][0-9]"? That should find all of the substrings that you are looking for.

answered Dec 25, 2012 at 1:41

hologram

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Community · Accepted Answer · 2020-06-20 09:12:55Z

0

^[a-z]{1}[0-9]{2}$

sedfdhajkldsfakdsakvsdfasdfr30.reed.op.1xp0

as far as i can read this

find thr first lower gives[s] caps letter after it there should be two numbers meaning the length of your string is and always will be 3 word chars

Maybe if i have more data about your string i can help

EDIT

if you are sure of *number of dots then

change this line

Matcher matcher = pattern.matcher("sedfdhajkldsfakdsakvsdfasdfr30.reed.op.1xp0");

to

Matcher matcher = pattern.matcher("sedfdhajkldsfakdsakvsdfasdfr30.reed.op.1xp0".split("\.")[0]);

note:-

using my solution you should omit the leading ^ for pattern

read this page for Spliting strings

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Dec 25, 2012 at 13:26

user1928148

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