这个函数有点方便哦 
        String str = scanner.next();
        String emailMatcher="[a-zA-Z0-9]+@[a-zA-Z0-9]+\\.[a-zA-Z0-9]+";  //不明觉厉
        if(str.matches(emailMatcher))
            System.out.println("邮箱格式合法");
        else
            System.out.println("邮箱格式不合法");