CODEWITHSUNDEEP
javaregex
Joel Christophel
Joel Christophel

Reputation: 2653

Start of String Java regex

I want to match an occurrence of 1 that comes after either the beginning of the String or a.

I've tried [\Aa]1, but this gives me a PatternSyntaxException.

Upvotes: 0

Views: 125

Answers (2)

p.s.w.g
p.s.w.g

Reputation: 148990

Try a pattern like this:

(^|a)1

The ^ will match the begining of the string, while the a will match a literal Latin letter a. The | is called an alternation, and will match either the pattern on the left or the right, while parentheses restrict the scope of the alternation.

Now, this will include the a as part of the matched string. If you'd like to avoid this you can either use a lookbehind, like this:

(?<=^|a)1

This will match a 1, but only if it is immediately preceeded by the beginning of the string or a Latin letter a.

Upvotes: 2

Pshemo
Pshemo

Reputation: 124215

I am not sure if that is what you mean but maybe you are looking for something like

(?<=\\A|a)1

or if you are not using Pattern.MULTILINE flag 

(?<=^|a)1

Upvotes: 1

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