Remove repeated characters in the string using Java Regular Expressions

String STR = "abcdeabcdeabcdeaaaaaadddddceeeeabcccccacadaeec ";
STR = Str. replaceall (Reg ,"");
System. Out. println (STR );

STR = Str. replaceall ("(? S )(.)(? =. * \ 1 )","");
(? S )(.)(? =. * \ 1)

(? S) enable the single-line mode dotall to match the. Number with any character
(.) Any character and captured in the first group
(? =. * \ 1) This is an assertion, indicating that the following content will be any character plus the content captured by the first group.

In this way, if the entire expression matches, it indicates that the content of the first capture group appears in the string at least twice and is replaced with "" empty string.

After global replacement, the characters in the entire string are not repeated.