Java Regex Matcher: Negative Lookaround Not Working

Question

I have a code that looks for Regex matches and adds a new line after the regex Match. This works on the first click of a button, but when I click it again, it still captures the regex.

Example Scenario:

Change all sentences ending with 'dog.' and add a new line if it is not the end of the line.

Sample code inside mouse click event:

Pattern pattern = Pattern.compile("dog\\.(?!\n)");
Matcher matcher = pattern.matcher(paragraph);
paragraph = matcher.replaceAll("dog\\.\n");

Sample Input:

I found a street animal. It was a dog. Then the dog found another dog. It was kind of fun to see the two dogs barking to each other.

First click of button that implements code:

I found a street animal. It was a dog. 
Then the dog found another dog. 
It was kind of fun to see the two dogs barking to each other.

Second click of button that implements code:

I found a street animal. It was a dog. 

Then the dog found another dog. 

It was kind of fun to see the two dogs barking to each other.

I'm quite confused on why on the second click, it fails to notice that there is no more instance of 'dog.' without a new line.

Thanks in advance for the help!

@SebastianProske Hi, the text is only inputted during runtime through SWT (Window Builder) textbox. — Kawamoto Takeshi
– Kawamoto Takeshi, Commented Jun 13, 2016 at 5:14
I have tried the code with string and it works as expected (on Windows). What is your OS? MacOS? Maybe SWT converts your \n to \r. Then this pattern should work dog\\.(?![\\n\\r]) — CoronA
– CoronA, Commented Jun 13, 2016 at 5:38

anubhava · Accepted Answer · 2016-06-13 12:58:15Z

1

You can use:

String str = 
"I found a street animal. It was a dog. \nThen the dog found another dog. \nIt was kind of fun to see the two dogs barking to each other."; 

Pattern pattern = Pattern.compile("(?<=dog\\.(?!\\s*\\n))\\s*");
Matcher matcher = pattern.matcher(str);
str = matcher.replaceAll("\r\n");

RegEx Demo

Code Demo

edited Jun 13, 2016 at 12:58

answered Jun 13, 2016 at 5:16

anubhava

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4 Comments

Kawamoto Takeshi Over a year ago

Hi, this code works. However, it does not work once I change the input string. Note that I am working with SWT, and I have a textbox where user can input paragraph and button that does the check. For example: I input the sample text. Clicked the button and it works, but when I append new lines to the first text and clicked the button again, it does not work and it removes all the spaces in the newly added text.

Kawamoto Takeshi Over a year ago

Hi, yes it does work if it's running only once. I have SWT Window Builder and I can change the text anytime during runtime. I have a textbox where user can input text. If user inputs text and clicks the button, it works but when user adds more text in the texbox and clicks the button, it doesnt work anymore.

Kawamoto Takeshi Over a year ago

Hi @anubhava , I have checked and it works fine when I print the result in console but it is not showing correctly in SWT textbox. Thanks.

Kawamoto Takeshi Over a year ago

Hi @anubhava, I found it out. SWT's new line is \r\n. That's why it only works once. Thanks!

Sanidhya Kumar · Accepted Answer · 2016-06-13 06:22:20Z

0

hope below code might help you..

    String paragraph = "I found a street animal. It was a dog. Then the dog found another dog. It was kind of fun to see the two dogs barking to each other.";
    paragraph = paragraph.replaceAll("dog\\.(?!\n)", "dog\\.\n");

thnx.

answered Jun 13, 2016 at 6:22

Sanidhya Kumar

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2 Comments

Alan Moore Over a year ago

Your solution is to switch from Matcher's replaceAll() method to String's replaceAll() method? How does that help?

Alan Moore Over a year ago

But that's all it does. Your suggestion is exactly the same as what the OP is already doing, only in one line instead of three. An answer should attempt to solve the problem posed in the question, and this one doesn't.

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