Find duplicate char sequences in String by regex in Java

Question

I have an input string and I want to use regex to check if this string has = and $, e.g:

Input:

name=alice$name=peter$name=angelina

Output: true

Input:

name=alicename=peter$name=angelina

Output: false

My regex does't work:

Pattern pattern = Pattern.compile("([a-z]*=[0-9]*$])*");
Matcher matcher = pattern.matcher("name=rob$name=bob");

Just split string by `$` and check – SomeDude Apr 13 '20 at 16:29 — SomeDude, Apr 13 '20 at 16:29

score 2 · Accepted Answer · answered Apr 13 '20 at 16:47

With .matches(), you may use

Pattern pattern = Pattern.compile("\\p{Lower}+=\\p{Lower}+(?:\\$\\p{Lower}+=\\p{Lower}+)*"); // With `matches()` to ensure whole string match

Details

\p{Lower}+ - 1+ lowercase letters (use \p{L} to match any and \p{Alpha} to only match ASCII letters)
= - a = char
\p{Lower}+ - 1+ lowercase letters
(?:\\$\\p{Lower}+=\\p{Lower}+)* - 0 or more occurrences of:
- \$ - a $ char
- \p{Lower}+=\p{Lower}+ - 1+ lowercase letters, = and 1+ lowercase letters.

See the Java demo:

List<String> strs = Arrays.asList("name=alice$name=peter$name=angelina", "name=alicename=peter$name=angelina");
Pattern pattern = Pattern.compile("\\p{Lower}+=\\p{Lower}+(?:\\$\\p{Lower}+=\\p{Lower}+)*");
for (String str : strs)
    System.out.println("\"" + str + "\" => " + pattern.matcher(str).matches());

Output:

"name=alice$name=peter$name=angelina" => true
"name=alicename=peter$name=angelina" => false

And when I have also "name=alice&name=" or "=alice&name=bob", how to add empty string in regex? — Alice Victoria, Apr 13 '20 at 17:31
@AliceVictoria Then use `*` quantifiers, https://ideone.com/p5mgo2 — Wiktor Stribiżew, Apr 13 '20 at 17:51

Pavneet_Singh · Answer 2 · 2020-04-13T16:31:52.860

You have extra ] and need to escape $ to use it as a character though you also need to match the last parameter without $ so use

([a-z]*=[a-z0-9]*(\$|$))*

• [a-z]*= : match a-z zero or more times, match = character

• [a-z0-9]*(\$|$): match a-z and 0-9, zero or more times, followed by either $ character or end of match.

• ([a-z]*=[a-z0-9]*(\$|$))*: match zero or more occurences of pairs.

Note: use + (one or more matches) instead of * for strict matching as:

([a-z]+=[a-z0-9]+(\$|$))*

Find duplicate char sequences in String by regex in Java

2 Answers2