Check if a String matches specific regular expression

Question

I am not so good with regular expressions and stuff, so I need help. I have to check if a input value matches a specific regular expression format. Here is the format I want to use, 25D8H15M . Here the D means the # of days H means hours and M means minutes. I need the regular expression to check the String. Thanks

Answer 1

Here's the briefest way to code the regex:

if (str.matches("(?!$)(\\d+D)?(\\d\\d?H)?(\\d\\d?M)?"))
    // format is correct

This allows each part to be optional, but the negative look ahead for end-of-input at the start means there must be something there.

Note how with java you don't have to code the start ( ^ ) and end ( $ ) of input, because String.matches() must match the whole string, so start and end are implied .

However, this is just a rudimentary regex, because 99D99H99M will pass. The regex for a valid format would be:

if (str.matches("(?!$)(\\d+D)?([0-5]?\\dH)?([0-5]?\\dM)?"))
    // format is correct

This restricts the hours and minutes to 0-59 , allowing an optional leading zero for values in the range 0-9 .

Answer 2

简化的正则表达式可以是：

^\\d{1,2}D\\d{1,2}H\\d{1,2}M$

Answer 3

Try,

    String regex = "\\d{1,2}D\\d{1,2}H\\d{1,2}M";
    String str = "25D8H15M";

    System.out.println(str.matches(regex));