pattern match get lastindex of a character

Question

the below will give me between _ and . for example Pet_you.txt will give me you

but if I get pet_te_you.txt will get te_you but instead I need you result. how to fix my pattern to take last _?

Pattern MY_PATTERN = Pattern.compile("\\_(.*?)\\.");
Matcher m = MY_PATTERN.matcher("pet_te_you.txt");
while (m.find()) {
    Type = m.group(1);
    System.out.println(dbType);
}

@antonyh the length character is not fix , if i said last index of _ then i will have you.txt . then how to remove the .txt ? — Moudiz, Jan 25 '18 at 11:27
Some of the answers such as those by notyou, Anirudh, yudong shen show how this is possible with lastIndexOf. You just have to do lastIndexOf twice (once for the _ and again for the .) — antonyh, Jan 25 '18 at 16:04

score 2 · Answer 1 · answered Jan 25 '18 at 11:26

2

You just have to avoid "_" in the capture pattern.

Pattern.compile("\\_([^_]+?)\\.")

answered Jan 25 '18 at 11:26

Dennis C

24,511
12
71
99

thanks its worled , but is it possible to have the result using lastindexof ? – Moudiz Jan 25 '18 at 11:29

score 2 · Accepted Answer · answered Jan 25 '18 at 12:25

As a non-regex pattern, you could use substring twice - once for the lastIndexOf("_") and then for the lastIndexOf(".").

s = s.substring(s.lastIndexOf("_") + 1);
s = s.substring(0, s.lastIndexOf("."));

Or a fun alternative to combine them both in a *non-ugly way:

s = s.substring(s.lastIndexOf("_") + 1).substring(0, s.substring(s.lastIndexOf("_") + 1).lastIndexOf("."));

Or perhaps, loop through the String in reverse (I used a StringBuilder), from lastIndexOf(".") - 1 until you reach a non-character (or perhaps a _).

for (int i = s.lastIndexOf(".") - 1; i > 0; i--) {
    if (Character.isAlphabetic(s.charAt(i))) {
        sb.append(s.charAt(i));
    } else {
        break;
    }
}

Here's an online example.

_{*This is definitely ugly}

score 1 · Answer 3 · answered Jan 25 '18 at 12:25

1

Same implementation using lastIndexOf

String text = "pet_te_you.txt";
System.out.println(text.substring(text.lastIndexOf("_")+1, text.lastIndexOf(".")));

answered Jan 25 '18 at 12:25

Anirudh

437
2
10

score 1 · Answer 4 · answered Jan 25 '18 at 12:26

you can match with look around: (?<=_)[^_]+(?=\.), and yes, you can have result using lastIndexOf too.

String as[] = {"pet_te_you.txt", "Pet_you.txt"};
Pattern p =  Pattern.compile("(?<=_)[^_]+(?=\\.)");
for (String s : as) {
    int beginIndex = s.lastIndexOf("_");
    int endIndex = s.lastIndexOf(".");
    if (beginIndex >= 0 && endIndex >= 0 && beginIndex < endIndex) {
        System.out.println(s.substring(beginIndex + 1, endIndex));
    }

    Matcher m = p.matcher(s);
    if (m.find()) {
        System.out.println(m.group());
    }
}

output:
    you
    you
    you
    you

pattern match get lastindex of a character

4 Answers4