public static String removeDuplicate(String s) {
StringBuilder builder = new StringBuilder();
char lastchar = '';
for (int i = 0; i < s.length(); i++) {
  String str = builder.toString();
  if (!str.equals("")
      && (str.charAt(str.length() - 1) == s.charAt(i))) {
    builder.deleteCharAt(str.length() - 1);
  } else if (s.charAt(i) != lastchar)
    builder.append(s.charAt(i));
  lastchar = s.charAt(i);
}
return builder.toString();
}

public static String removeDuplicates(String s) {
    if (s.isEmpty()) {
        return s;
    }
    char[] buf = s.toCharArray();
    char lastchar = buf[0];

    // i: index of input char
    // o: index of output char
    int o = 1;
    for (int i = 1; i < buf.length; i++) {
        if (o > 0 && buf[i] == buf[o - 1]) {
            lastchar = buf[o - 1];
            while (o > 0 && buf[o - 1] == lastchar) {
                o--;
            }
        } else if (buf[i] == lastchar) {
            // Don't copy to output
        } else {
            buf[o++] = buf[i];
        }
    }
    return new String(buf, 0, o);
}

public class Test3 {
    public static void main(String[] args) {
        String str = "ABBCDAABBBBBBBBOR";
        char[] ca = str.toCharArray();

        Arrays.sort(ca);

        String a = new String(ca);
        System.out.println("original => " + a);
        int i = 0 ;
        StringBuffer sbr = new StringBuffer();
         while(i < a.length()) {
             if(sbr.length() == 0 ) {sbr.append(a.charAt(i));}
             if(a.charAt(i) == sbr.charAt(sbr.length() -1)) {i++ ;}
             else {sbr.append(a.charAt(i));}
         }//while

         System.out.println("After removing the duplicates => " + sbr);
    }//main
}// end1