public static void main(String[] args) {
        String s = "aaaa......bbbb....ccc...dddddd";
        String s2 = s.replaceAll("\\.+","");
        System.out.println(s2);                                     // s2:aaaabbbbcccdddddd
        String s3 = s2.replaceAll("(.)\\1+","$1");  // $1代表第一組中的內容
        System.out.println(s3);                                     //
 
s3:abcd
    }