Java RegEx - 检查字符串是否以确切的位数结尾

Question

The Java matches method returns 'true' for all of the following

// check if a string ends with an exact number of digits (yyyyMMdd 8 digits)

    String s20180122_1 = "fileNamePrefix_20171219";
    String s20180122_2 = "fileNamePrefix_20171219131415111";

    System.out.println(s20180122_1.matches(".*\\d{8}$"));
    System.out.println(s20180122_2.matches(".*\\d{8}$"));
    System.out.println(s20180122_2.matches(".*\\d{8,8}$"));

Since the s20180122_2 has more digits I expect the 2nd and 3rd checks to return 'false', but they don't. How do I enforce the exact (8 digits only. No more, no less) match?

Thanks for your help.

Answer 1

This should work:

.*[^\d]\d{8}$

or if Java regex engine supports \\D group, you can use it instead of [^\\d]

Answer 2

这个正则表达式将验证最后8个字符是yyyyMMdd形式的数字（年份在yyyyMMdd世纪之内：

.*[^\d](19|20)\d{2}(0[1-9]|1[0-2])(0[1-9]|[12]\d|3[01])$