java String.replaceAll regex question

Question

I have a string that contains the following text

String my_string = "hello world. it's cold out brrrrrr! br br";

I'd like to replace each isolated br with <br />

The issue is that I'd like to avoid converting the string to

"hello world. it's cold out <br />rrrrr! <br /> <br />";

What I'd like to do is convert the string (using replaceAll) to

"hello world. it's cold out brrrrrr! <br /> <br />";

I'm sure this is very simple, but my regex isn't correct.

my_string.replaceAll("\\sbr\\s|\\sbr$", "<br />");

my regex is supposed to find 'whitespace' 'b' 'r' 'whitespace' OR 'whitespace' 'b' 'r' 'end of line'

but it misses the final "br" in my string

"hello world. it's cold out brrrrrr!<br />br"

what am I doing wrong?? TKS!

"hello world. it's cold out brrrrrr!<br />br" Your final 'br' isn't preceded by whitespace. — Tony Ennis
– Tony Ennis, Commented Oct 14, 2010 at 17:38

kennytm · Accepted Answer · 2010-10-14 17:20:32Z

8

Use

my_string.replaceAll("\\bbr\\b", "<br />");

Your regex doesn't work because in

␣br␣br
^

The pattern \sbr\s will consume the whole ␣br␣, leaving with

<br />br
      ^

now there is no preceding space for this br to match \sbr$, so it will be missed.

On the other hand, the \b, meaning a word-boundary, is a zero-width assertion, i.e. it won't consume any characters. Therefore the spaces will be kept and all isolated br's will be matched.

answered Oct 14, 2010 at 17:20

kennytm

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10 Comments

user141146 Over a year ago

ok, so let me see if i get this straight... \b is word boundary, right? and apparently it works on "end of line" too?

Alan Moore Over a year ago

The end of a line is a word boundary if the last character in the line is a word character:. More info: regular-expressions.info/wordboundaries.html

kennytm Over a year ago

@Tony: not reproducible. What kind of Java are you using?

Tony Ennis Over a year ago

Comment deleted. I didn't notice the OP's string didn't meet his own criteria about leading whitespace.

kennytm Over a year ago

@Tony: This is because < and b form a word boundary. Since OP doesn't specify what to do in this case, I don't think it is a "bad" result.

|

Tony Ennis · Accepted Answer · 2010-10-14 17:39:39Z

0

"hello world. it's cold out brrrrrr!<br />br" Your final 'br' isn't preceded by whitespace. What's supposed to happen?

answered Oct 14, 2010 at 17:39

Tony Ennis

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