8VaYLJZp

1Set<String> users = new HashSet<>(); // to avoid repeated mentions
2    for (Tweet t: tweets){
3        String line = t.getText();
4        String pattern = "(?<=^|(?<=[^a-zA-Z0-9-_\.]))@[A-Za-z0-9_-]+";
5        Pattern p = Pattern.compile(pattern);
6        Matcher m = p.matcher(line);
7        if (m.find()){
8            users.add(m.group().toLowerCase()); 
9        }
10	
11@tony
12$$@yahoo$$
13john @john john
14@joules-
15@john-cassidy
16%%@jake%%
17@@@jake@@@
18dude$@jake$$
19$$$@jack$$$
20@@@jake@@@ 
21@john4 
22@jake2$
23@johN3 
24@rock-smith
25@John 
26@gmail.com //should not return but does: wrong
27richard@mit.edu //should not find and it doesn't: good