import java.util.regex.*;

public class TestMatches 
{
	public static void main(String[] args)
	{
		String[] mails=
			{
				"aaaaa@163.com","jjjjjjjjjj@gmail.com","kkkkkkkk@onnnn.cn","wawa@abc.xx"
			};
		String mailRegEx="\\w{3,20}@\\w+\\.(com|org|cn|net|gov)";//{3,20}表示3~20个字符
		Pattern mailPattern=Pattern.compile(mailRegEx);
		Matcher matcher=null;
		for(String mail : mails)
		{
			if(matcher==null)
			{
				matcher=mailPattern.matcher(mail);
			}
			else
			{
				matcher.reset(mail);
			}
			if(matcher.matches())
			{
				System.out.println(mail+"是一个有效的邮件地址");
			}
			else
			{
				System.out.println(mail+"不是一个有效的邮件地址");
			}
		}
	}
}