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I have a string of comma separated words e.g. "a, b, c".
I need to replace the last comma instance with “and”, to make it look like "a, b and c".

I've tried using replaceFirst like this: 

"a, b, c".replaceFirst("(,)[^,]+$", " and")

But it doesn't work. It replaces everything after the last comma with “and” rather than just the comma producing "a, b and".

How to make it work?
I'm on java8.

Ps. I thought that it's obvious, but it seems like I need to clarify, that I'm looking for a generic solution that works with any number of comma separated tokens, i.e. 'a, b, ...., c'

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6
  • 3
    String's 'lastIndexOf' would help Commented Apr 6, 2017 at 6:21
  • i'm also thinking of lastIndexOf but it can't be use on replace right? Commented Apr 6, 2017 at 6:24
  • 2
    Use "a, b, c".replaceFirst(",([^,]+)$", " and$1") Commented Apr 6, 2017 at 8:13
  • @Holger haha,we are the same. Commented Apr 6, 2017 at 8:31
  • 1
    @holi-java: I already noticed. It’s the most straight-forward way to fix the question’s approach, imho. Commented Apr 6, 2017 at 8:33

3 Answers 3

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12

I don't think you need anything particular from Java 8 here. If you want to go the regex route with String#replaceAll(), then you can consider using the following pattern:

(.*), (.*)

Simple rebuild the string using the first and second capture groups, with and in between them. The first pattern (.*) will greedily consume everything until the last comma, exactly the behavior you want. Then, the second (.*) does cleanup to capture the final letter/string.

String input = "a, b, c";
input = input.replaceAll("(.*), (.*)", "$1 and $2");
System.out.println(input);

Output:

a, b and c
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1 Comment

You might add why it works: The first .* is greedy, so consumes all but the last ,. (Well, they're both greedy, but the earlier one gets to be greedy first.)
8

I think the replaceFirst is better than replaceAll for you because you want to replace only once not all, and it run faster than replaceAll.

  1. using ${number} to capturing groups. 

    "a, b, c".replaceFirst(",([^,]+)$", " and$1"); // return "a, b and c"

  2. using positive lookahead:

    "a, b, c".replaceFirst(",(?=[^,]+$)", " and"); // return "a, b and c"
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4 Comments

I did not down-vote, but that replaceFirst is quiet misleading; it's actually a single replace there... May be replacing with replaceAll would make more sense.
@Eugene I think replaceFirst better meaniful than replaceAll, because OP want to replace once. thanks, I want to know why vote it down.
@Holger I don't care about the votes, I want to know why vote it down? can you tell me why?
@Holger I have removed it from answer, You may have misunderstood me. I just want to know why ? and learning more from why vote it down.
2

You can also achieve same thing using lastIndexOf :

String str = "a, b, c";
StringBuilder builder = new StringBuilder(str);
int lastindex = str.lastIndexOf(",");
builder.replace(lastindex, lastindex + 1, " and" );
System.out.println(builder.toString());

Output:

a, b and c
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1 Comment

Sometimes, a lightweight StringBuilder operation might be preferable to a regex manipulation, but then, it would be more efficient to use partial copying instead of copying the entire string and shifting content: int lastindex = str.lastIndexOf(','); String result = new StringBuilder(str.length()+3) .append(str, 0, lastindex).append(" and") .append(str, lastindex+1, str.length()) .toString();

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