java - Regex repeated character (\\1 doesn't work) -

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• why doesn't regex work expected in java? 3 answers

i'm trying make regex in java returns true if repeated characters present in input string , false otherwise, regex short possible (for code-golf challenge). i'm not @ regexes, thought trick:

(.)\\1 

where (.) character , \\1 reference match found in first part of regex.

however, if try input "1223", doesn't work:

public static void main(string[] a){      system.out.println(java.util.regex.pattern.matches("(.)\\1", "1223")); } 

this return false, while i'm expecting true because of 22.

does know how fix regex using java.util.regex.pattern.matches, or shorter, since it's code-golf? ;)

here ideone test.

matches consumes whole string: first . matches "1", \\1 attempts match "1" next character, , fails.

you have 2 options:

• use find, or
• change regex .*(.)\\1.*

explanation:

the second option works because .* first match whole string, it'll fail match \\1, backtracks char char until .* matched "1", (.)\\1 match "22", , final .* match rest of string.