Java regex replace repeated characters (including non consequent)

Question

I'm trying to write a regular expression to replace first among repeated characters in a string.

The catch is the repeated characters can also be non-consequent.

    Ex: 

    Input: abcdebg
    Replace by character:  x
    Expected Output: axcdebg

I have been trying to do this with a regular expression: (.).*(\\1) But the result when i do a replace is: axg

Please suggest how i can achieve the expected result.

Thanks,
Sash

Could you explain first among repeated characters in a string ? — user2705585
– user2705585, Commented Mar 24, 2016 at 10:39
@noob In the given example 'b' is a repeated character , i actually want to replace one of the occurence of 'b' — Pruthvi Raj Nadimpalli
– Pruthvi Raj Nadimpalli, Commented Mar 24, 2016 at 10:41

Evan Knowles · Accepted Answer · 2016-03-24 10:43:13Z

2

The problem here is that you're matching the rest of the string up until the repeated character as well, which means it's also being replaced. You'll need to capture it and include it again.

So,

regex: (.)(.*?\\1)

Replace with (for x): x\2

answered Mar 24, 2016 at 10:43

Evan Knowles

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2 Comments

Pruthvi Raj Nadimpalli Over a year ago

Thanks for quick answer. I tried (.)(.*?\\1) and the replaceFirst still gives me wrong answer (same as mine): axg

Pruthvi Raj Nadimpalli Over a year ago

Bro, sorry i tried replaceAll with x$2 and it looks like it works. Let me try with couple of inputs and i'll accept your answer. Thank you

anubhava · Accepted Answer · 2016-03-24 11:11:23Z

0

You can use this lookahead based regex to replace a character only if same character is found ahead in input:

String str = "abcdebg";
String repl = str.replaceFirst("(.)(?=.*\\1)", "x");
//=> axcdebg

answered Mar 24, 2016 at 11:11

anubhava

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