replaceAll method regex

Question

My sample input is "0X10001,0X10002,0X610001,0X610002"

System.out.println(st.replaceAll(regex, "0"));

My output should be "010001,010002,610001,610002"
0X should be replaced by
0 --> if length is 7
""--> if length is 8

what is the regex I have to use?
([0X]){1,2} not getting desired output by this.

Post the regex that you already have and that you want to improve upon. — chb, Jan 07 '19 at 05:59
do two separate replaces: First one replace `0X(\d{5})` to `0$1`, second one replace `0X(\d{6})` to `$1` — Adrian Shum, Jan 07 '19 at 06:20
@AdrianShum You'll want to switch the order and/or check for word boundaries. — shmosel, Jan 07 '19 at 06:24
@Adrian Shum thank you, when I use two replaces like this System.out.println(st.replaceAll("0X(\\d{5})", "0$1").replaceAll("0X(\d{6})", "$1")); it is showing error (saying I should use \b,\n...…) in eclipse — Tej4493, Jan 07 '19 at 06:37
@shmoesel: yes I was intentionally not giving the full regex, but just giving basic idea (and was expecting OP to write his own) — Adrian Shum, Jan 07 '19 at 06:38

Andreas · Answer 1 · 2019-01-07T06:39:33.007

Do it like this:

String st = "0X10001,0X10002,0X610001,0X610002";
System.out.println(st.replaceAll("0X(?=\\d{6})|(0)X(?=\\d{5})", "$1"));

Output

010001,010002,610001,610002

Explanation

As the regex engine scans, the pattern | will always try left side before right side, so as it advances, it will first it try 0X(?=\\d{6}), which is a match for 0X followed by 6 digits (using zero-width positive look-ahead). If that matches, nothing is captured, so $1 is empty, and 0X is replaced by empty string.

If that didn't match, it tries (0)X(?=\\d{5}), i.e. match 0X followed by 5 digits. If that matches, the 0 is captured in group 1, so $1 is 0, and 0X is replaced by 0.

If neither match, the regex engine will try again at the next position in the input string.

tricky but interesting :) – Adrian Shum Jan 07 '19 at 06:39 — Adrian Shum, Jan 07 '19 at 06:39
thank you for the explanation and answer @Andreas – Tej4493 Jan 07 '19 at 06:54 — Tej4493, Jan 07 '19 at 06:54

score -2 · Answer 2 · edited Jan 07 '19 at 09:29

-2

replaceAll("0X(?=\\d{6})|(0)X(?=\\d{5})", "$1") works fine for the given issues

edited Jan 07 '19 at 09:29

Raibaz

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answered Jan 07 '19 at 06:58

Tej4493

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replaceAll method regex

2 Answers2