Qq mail Regular Expression

For the regular expression of the mailbox, you must first confirm the mailbox registration rules!
Qq mail registration rules:

1. It must start with a-z English letter (case-insensitive)
2. It consists of 3-18 English letters, numbers, minus signs, and underscores.
3. Domain Name: qq.com or QQ.com
The regular expression is:
String regex = "[a-zA-Z] [a-zA-Z_-0-9] {} @ (qq | QQ). cn"
String mailname = "sunfei@qq.com ";
Pattern pattern = Pattern. compile (regex );
Matcher matcher = pattern. matcher (mailname );
System. out. println (matcher. matches ());