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

@Bohemian, what I need to do is: check if the given string is valid, valid values are: 1D - 2D15H - 5H33M - 22D30M - 15D12H45M etc. — Shahe Masoyan
– Shahe Masoyan, Commented Nov 26, 2013 at 13:15
So all parts are optional, but there must be at least one part? Is 3D5M valid? Is there a maximum number value for the days part? — Bohemian
– Bohemian ♦, Commented Nov 26, 2013 at 13:20
OK - see my updated answer that meets your extended requirements — Bohemian
– Bohemian ♦, Commented Nov 26, 2013 at 13:29

Bohemian · Accepted Answer · 2013-11-26 13:28:51Z

19

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.

edited Nov 26, 2013 at 13:28

answered Nov 26, 2013 at 12:59

Bohemian♦

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Comments

anubhava · Accepted Answer · 2013-11-26 12:50:49Z

1

A simplified regex can be:

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

answered Nov 26, 2013 at 12:50

anubhava

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2 Comments

Shahe Masoyan Over a year ago

thanks @anubhava for the answer, I have a question though, what does the numbers in the curly brackets mean?

anubhava Over a year ago

\\d{1,2} means match 1 or 2 digits these numbers mean lower limit and upper limit of # of matched patterns.

Masudul · Accepted Answer · 2013-11-26 13:05:34Z

1

Try,

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

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

edited Nov 26, 2013 at 13:05

answered Nov 26, 2013 at 12:53

Masudul

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6 Comments

anubhava Over a year ago

It will also match 111125D8H15MMMM

Masudul Over a year ago

@anubhava, nope, I have just tested.

anubhava Over a year ago

String#matches adds ^ and $ but if same regex is used in Pattern then it will match bigger string.

Bohemian Over a year ago

@anubhava 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

Bohemian Over a year ago

@Masud the character classes are unnecessary here, ie \\d{1,2} is identical to [\\d]{1,2} because there's only one character (type)

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