java regex matches loop in reverse direction

Question

I want to match regex pattern in java for particular text. In that while matching I need to find matches in reverse order.

Example:

Regex Pattern --  [([^]]*])

Input String  -- [blue][red][green]

Output   --  1st match --->[blue]
             2nd match --->[red]
             3rd match --->[green]

But I'm expecting match to be in reverse order.

Expected output  --    1st match --->[green]
             2nd match --->[red]
             3rd match --->[blue]

Please help how to form the regex to achieve the expected output.

@ScaryWombat StringBuilder.reverse will reverse the String as whole like this ]neerg[]der[]eulb[. I don't know how it will solve my problem. Please explain me — Roshan, Sep 28 '16 at 02:36
Now i achieved by saving matches in ArrayList and reverse the List to get Expected output. But I need to do it in regex part itself. Because in case they are more than 10 matches I need only 10 matches from the last. So I iterate the reverse List for the size upto 10 and break the loop. I don't need to grow list size as it may contain 100 or 1000 matches. I need only last 10. — Roshan, Sep 28 '16 at 02:40
That regex doesn't work unless you add some escapes. `[([^]` is a character group matching `(`, `[` or `^`. Next is `]*` matching 0 or more `]`. Next is `]` matching exactly one `]`. Last is `)` which causes `PatternSyntaxException: Unmatched closing ')'`. — Andreas, Sep 28 '16 at 03:17
This can be done is a single regex, if you don't mind making it large. See [regex101](https://regex101.com/r/6h6txr/1) for demo. — Andreas, Sep 28 '16 at 03:23
in case of 10 the regex looks ok. In case,if my logic shifts to 50 or 100 then it is unmaintainable — Roshan, Sep 28 '16 at 05:11

score 1 · Answer 1 · answered Jan 14 '17 at 19:59

Assuming you have complied regex date"

     ArrayList<String> strings = new ArrayList<>();
            Matcher foo = date.matcher("foo");
            while (foo.matches()) {
                strings.add(foo.group());
            }
            Collections.reverse(strings);

score 0 · Answer 2 · edited May 23 '17 at 11:52

Reverse regular expression in Java discusses the topic and I posted a solution there, added here for convenience.

If anyone is interested in a Java solution, I implemented a library to do just that. https://github.com/vsch/reverse-regex.

Handles all valid Java regex constructs and provides utility classes to wrap pattern, matcher and input for reverse searches to handle all need mappings and reversals.

java regex matches loop in reverse direction

2 Answers2