缺少一个括号，就会报错。
Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '*' near index 17 \w+@\w+(\.\w{2,3}*\.\w{2,3} ^ at java.util.regex.Pattern.error(Unknown Source) at java.util.regex.Pattern.sequence(Unknown Source) at java.util.regex.Pattern.expr(Unknown Source) at java.util.regex.Pattern.group0(Unknown Source) at java.util.regex.Pattern.sequence(Unknown Source) at java.util.regex.Pattern.expr(Unknown Source) at java.util.regex.Pattern.compile(Unknown Source) at java.util.regex.Pattern.(Unknown Source) at java.util.regex.Pattern.compile(Unknown Source) at java.util.regex.Pattern.matches(Unknown Source) at java.lang.String.matches(Unknown Source) at e5_17.Judge.main(Judge.java:11)
