Use Java regular to remove repeated characters from strings

String str = "abcdeabcdeabcdeaaaaaadddddceeeeabcccccccacadaeec";
str = str.replaceAll(reg, "");
System.out.println(str);

str = str.replaceAll(" (?s)(.)(?=.*\\1)", "");
(?s)(.)(?=.*\1)

(?s) Turn on the single-line mode DOTALL and let the . sign match any character
(.) any character and capture it in the first group
(?=.*\1) This is an assertion, indicating that the following content will be any number of characters plus the first A set of captured content

Like this, if the entire formula matches, it means that the first capture group content appears at least twice in the string and is replaced with "" empty string.

After global replacement, the characters appearing in the entire string will not be repeated.

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