Java removes duplicate characters from a string

The basic two methods
1, the use of regular expressions.

public string Removeduplicatechars (String str) {    return Str.replaceall ("(? s)" (.) (? =.*\\1) "," ");}

(? s) turn on single-line mode Dotall let. Number match any character
(.) Any character and capture the first set of
(? =.*\1) This is the assertion that the next content will be any character plus the first set of captured content, if this entire expression matches to, represents, the first capturing group content in the string, at least two occurrences, replaced by "" empty string. After a global substitution, the characters that appear throughout the string are not duplicated.

2, use traversal.

public string Removeduplicatechars (String str) {    string[] STRs = Str.split (""); It means you can't understand this place, why cut    list<string> List = new arraylist<string> () with an empty string;    StringBuffer buffer = new StringBuffer ();    for (stirng s:strs)    {        if (!list.contains (s))        {            list.add (s);            Buffer.append (s);        }    }    return buffer.tostring ();}

Java removes duplicate characters from a string