How to use regex non capturing group for string replace in java

Question

I had a requirement to change AssemblyVersion on new build. I do it using java code string.replaceAll(regexPattern,updatedString);

This code works fine with normal regex patterns, but I am not able to use non-capturing groups in this pattern. I want to use non-capturing groups to make sure I don't capture patterns other than required one. This is the code I tried:

String str="[assembly: AssemblyVersion(\"1.0.0.0\")]";
str=str.replaceAll("(?:\\[assembly: AssemblyVersion\\(\"\\d\\.\\d\\.)?.*(?:\"\\)\\])?", "4.0");
System.out.println(str);

Here, I want to match string [assembly: AssemblyVersion(int.int)] and replace only minor version.

Expected outcome is [assembly: AssemblyVersion("1.0.4.0")], but I'm getting result as 4.04.0.

Can anyone please help me on this?

I ran this and you don't have any groups in that pattern. Are you looking to use capturing groups? — MadConan
– MadConan, Commented May 15, 2015 at 13:28
[assembly: AssemblyVersion("1.0 This I want as non capturing group 0.0 I want as capturing group ")] I want as non capturing group. So that only bug fix number (third digit) and build number (fourth digit) gets replaced but whole pattern is used for matching. — Pramod Jangam
– Pramod Jangam, Commented May 15, 2015 at 13:34

Mena · Accepted Answer · 2019-09-03 08:34:51Z

9

Why not use look-ahead / look-behind instead?

They are non-capturing and would work easily here:

str = str
    .replaceAll(
        "(?<=\\[assembly: AssemblyVersion\\(\"\\d\\.\\d\\.).*(?=\"\\)\\])",      
        "4.0"
    );

edited Sep 3, 2019 at 8:34

answered May 15, 2015 at 13:37

Mena

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1 Comment

cary m Over a year ago

The reason this works and your example didn't is because your call String.replaceAll() doesn't use capturing groups. What replaceAll() does is take everything that matches the regex and replace it with the replacement value. Look-(ahead/behind) will do what you want because they're "zero-length" assertions: the regex will only match your string if the look-ahead behind is there, but those parts of the pattern won't "count" as part of the matched String, so they won't be replaced.

Wiktor Stribiżew · Accepted Answer · 2015-05-15 13:41:35Z

1

As an alternative to a look-behind, you can use capturing groups around what you want to keep, and keep what you want to replace in a non-capturing group or no group at all:

String str="[assembly: AssemblyVersion(\"1.0.0.0\")]";
str=str.replaceAll("(\\[assembly:\\s*AssemblyVersion\\(\"\\d+\\.\\d+\\.)\\d+\\.\\d+(?=\"\\)\\])", "$014.0");
System.out.println(str);

See IDEONE demo

answered May 15, 2015 at 13:41

Wiktor Stribiżew

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Comments

MadConan · Accepted Answer · 2015-05-15 13:47:12Z

0

This worked for your case:

str.replaceAll("(\\[assembly: AssemblyVersion\\(\"\\d\\.\\d\\.)(\\d\\.\\d)(\"\\)\\])", "$14.0$3");

answered May 15, 2015 at 13:47

MadConan

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