replacing string with regex in java

Question

I think I have a decent handle wrt matching strings using Regex in Java, but now I am trying to replace strings using Regex and not having much success.

Simply put, I am trying to find where there is a digit immediately followed by a constant string "CMR", then adding a space between the digit and the "CMR" substring. "0CMR" should become "0 CMR", "5CMR" should become "5 CMR", etc. Any preceding non-digit should be left as it was.

So my source string is "theStringThat0CMRhas"

my command is:

replaceAll("[0-9]CMR", "[0-9] CMR");

I get the added space in the result, but the result becomes "theStringThat[0-9] CMRhas" which obviously isn't what I need. Somehow I need to tell Regex not to replace with "[0-9]", but with whatever it matched on in the first place.

I know I'm doing this wrong, but I don't know what's right.

Any help appreciated.

Thanks,

Tom

stackoverflow.com/q/988655/438992 and so on; searching the web for this turns up plenty of information. — Dave Newton
– Dave Newton, Commented Jan 9, 2017 at 3:25

Hulk · Accepted Answer · 2017-01-09 10:59:47Z

10

You want to use a capturing group:

replaceAll("([0-9])CMR", "$1 CMR")

$1 references the first group in the match, denoted by parentheses.

Also, [0-9] can be substituted with \d.

edited Jan 9, 2017 at 10:59

Hulk

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answered Jan 9, 2017 at 3:24

shmosel

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2 Comments

user5287318 Over a year ago

Can you add some description and instructions explain how this works? As a Java beginner won't understand what are you typing about.

Tom Over a year ago

Perfect answer, @shmosel. Not only showed the solution, but included the name and url of the description where I can go for more in-depth knowledge of the subject. Thanks muchly!

Gurwinder Singh · Accepted Answer · 2017-01-09 03:57:27Z

1

Try this:

replaceAll("(?<=\\d)(?=\\D)"," ")

It uses look ahead for non digit character and negative look ahead for digit characters.

If you want just do it for the one with CMR after the digits, use:

"(?<=\\d)(?=CMR)"

edited Jan 9, 2017 at 3:57

answered Jan 9, 2017 at 3:24

Gurwinder Singh

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Comments

Kaka Hoang Huy · Accepted Answer · 2017-01-09 03:26:33Z

0

You should group the number regex and call argument. Your code here:

replaceAll("([0-9])CMR", "$1 CMR");

For more regex knowledge, please read this document https://www.tutorialspoint.com/java/java_regular_expressions.htm

Good luck!

answered Jan 9, 2017 at 3:26

Kaka Hoang Huy

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Aurme Erebos · Accepted Answer · 2017-01-09 03:50:30Z

a good starting point may be here for reading regex: http://www.regular-expressions.info/java.html

on this site the replacing string page is here: http://www.regular-expressions.info/replacetutorial.html

$with a number represents a whole regex match, and you can use these to refer to what you were doing

    String testString = "theStringThat0CMRhas";
    String resultString = testString.replaceAll("[0-9]CMR","$0");
    System.out.println(resultString);

this would result in the answer: theStringThat0CMR has

you obviously didnt want this, so lets change the answer up a little

    String testString = "theStringThat0CMRhas";
    String resultString = testString.replaceAll("([0-9])CMR","$0 CMR");
    System.out.println(resultString);

now we are referencing the parenthsis, in which it hasn't done anything yet, so its replacing what it found, with the same thing, a space, and CMR

your result would now be: theStringThat0CMR CMRhas

so lets reference the part where we have chosen the number

    String testString = "theStringThat0CMRhas";
    String resultString = testString.replaceAll("([0-9])CMR","$1 CMR");
    System.out.println(resultString);

now your answer will be: theStringThat0 CMRhas

it is finding where it picked a number, replacing it with that number, a space, and then CMR

you are trying to do what I believe to be called a backreference though I am unsure. Regex is still not my strong suit either.

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