Split string in reverse

Question

I have a string sub1-sub2-sub3 which I want to split from right to left. Currently I am using split function like this which splits the string from left to right -

String str = "sub1-sub2-sub3";
System.out.println("Result :" + str.split("-", 2));

Elements in output :

sub1
sub2-sub3

Desired output :

sub1-sub2
sub3

Is there a way where I can split my string on - starting from right?

@jorn reversing the list would still give me the same elements but in reversed order. — darecoder, Apr 08 '22 at 09:57
@TimBiegeleisen I have some business logic I need the ```sub1-sub2``` part for some validation. I don't care how many ```-``` are in the string, but all I need is to split it in two parts. One should be the first from right and second should be the rest. — darecoder, Apr 08 '22 at 09:59
Why not just use lastIndexOf() and substring yourself on that? — GhostCat, Apr 08 '22 at 10:04

score 3 · Answer 1 · answered Apr 08 '22 at 10:02

3

You could do a regex split on -(?!.*-):

String str = "sub1-sub2-sub3";
String[] parts = str.split("-(?!.*-)");
System.out.println(Arrays.toString(parts));  // [sub1-sub2, sub3]

The regex pattern used here will only match the final dash.

answered Apr 08 '22 at 10:02

Tim Biegeleisen

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Arun Gowda · Answer 2 · 2022-04-08T11:45:01.440

2

A generic solution as utility method that takes limit as input with java 8:

public List<String> splitReverse(String input, String regex, int limit) {
    return Arrays.stream(reverse(input).split(regex, limit))
            .map(this::reverse)
            .collect(Collectors.toList());
}

private String reverse(String i){
    return new StringBuilder(i).reverse().toString();
}

reverse() code taken from here

Input: sub1-sub2-sub3

Reverse input: 3bus-2bus-1bus

Split(rev,2): [3bus] , [2bus-1bus]

Reverse each: [sub3] , [sub1-sub2]

edited Apr 08 '22 at 11:45

answered Apr 08 '22 at 10:19

Arun Gowda

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You might want to add the significant performance impact, compared to a straight forward solution that splits on a more complicated regex or that simply uses lastIndexOf() and substring. – GhostCat Apr 08 '22 at 10:45
Agreed. But `lastIndexOf` hardwires the limit to 2 which doesn't make justice to the question title. – Arun Gowda Apr 08 '22 at 10:55
Well, the question isn't really clear what the user would expect for a-b-c-d to happen ... – GhostCat Apr 08 '22 at 10:57

score 1 · Answer 3 · answered Apr 08 '22 at 10:06

One way would be to reverse the string before the split and then reverse the resulting strings.

String str = "sub1-sub2-sub3";
Arrays.stream(StringUtils.reverse(str).split("-",2))
      .map(StringUtils::reverse)
      .forEach(System.out::println);

Output:

sub3
sub1-sub2

It won't yield the same result as requested but maybe it will help.

P.S. util class used is from apache: org.apache.commons.lang3.StringUtils

score 0 · Answer 4 · answered Apr 08 '22 at 09:59

0

A quick and dirty solution i cam up with would be

    String str = "sub1-sub2-sub3";
    str = StringUtils.reverse(str);

    String[] split = str.split("-", 2);
    split[0] = StringUtils.reverse(split[0]);
    split[1] = StringUtils.reverse(split[1]);

    System.out.println("Result :" + split[0] + " #### " + split[1]);

another way would be java how to split string from end

answered Apr 08 '22 at 09:59

GJohannes

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import org.apache.commons.lang3.StringUtils; – GJohannes Apr 08 '22 at 11:48

score 0 · Answer 5 · answered Apr 08 '22 at 10:50

0

The below solution worked for me fine :

str.substring(0, str.lastIndexOf("-"));
str.substring(str.lastIndexOf("-"));

answered Apr 08 '22 at 10:50

darecoder

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Split string in reverse

5 Answers5