Java - How do i find out that a string is in the correct format using pattern matching

Question

My string value;

09:00-10:00,12:00-14:30,16:00-18:00 (this string repeats time intervals n times like this)

and I want to find out that a string is in the correct format using pattern matching;

Pattern.matches("<Pattern Here>", stringValue);

is it possible?

I tried;

Pattern.matches("^[0-9:0-9-0-9:0-9,]+$", value);

But doesn't work properly

Answer 1

You can check if the string matches the regex, ^(?:(?:\d{2}:\d{2}\-\d{2}:\d{2})(?:,(?!$))?)*$. Note that you do not need to put starts-with (i.e. ^) and ends-with (i.e. $) when using String#matches.

If the string passes this validation, split the string on , and - and then use java.time API to validate the individual time strings.

Demo:

import java.time.LocalTime;
import java.time.format.DateTimeParseException;

public class Main {
    public static void main(String[] args) {
        // Test
        System.out.println(hasCorrectFormat("09:00-10:00,12:00-14:30,16:00-18:00")); // true
        System.out.println(hasCorrectFormat("09:00-10:00,12:00-1:30,16:00-18:00")); // false -> 1:30 is not in desired
                                                                                    // format
        System.out.println(hasCorrectFormat("09:00-10:00")); // true
        System.out.println(hasCorrectFormat("09:00 10:00")); // false
        System.out.println(hasCorrectFormat("09:00-10:00,09:00 10:00")); // false
        System.out.println(hasCorrectFormat("09:00-10:00-12:00-14:30,16:00-18:00")); // false
        System.out.println(hasCorrectFormat("09:00-10:00,12:00-14:30,16:00-18:00,")); // false
    }

    static boolean hasCorrectFormat(String strTimeRanges) {
        if (!strTimeRanges.matches("(?:(?:\\d{2}:\\d{2}\\-\\d{2}:\\d{2})(?:,(?!$))?)*"))
            return false;
        String[] times = strTimeRanges.split("[-,]");
        for (String time : times) {
            try {
                LocalTime.parse(time);
            } catch (DateTimeParseException e) {
                return false;
            }
        }
        return true;
    }
}

Output:

true
false
true
false
false
false
false

Regex demo

Learn more about the modern Date-Time API from Trail: Date Time.

---

The valuable comment from Ole V.V. has prompted me to extend my original answer to show how one can use java.time API to compare the times in individual time ranges. I hope this gives enough hints for learners to extend the solution further based on the complexity of the requirements.

import java.time.LocalTime;
import java.time.format.DateTimeParseException;

public class Main {
    public static void main(String[] args) {
        // Test
        System.out.println(hasCorrectFormatAndRanges("09:00-10:00,12:00-14:30,16:00-18:00")); // true
        System.out.println(hasCorrectFormatAndRanges("09:00-10:00,12:00-1:30,16:00-18:00")); // false -> 1:30
        System.out.println(hasCorrectFormatAndRanges("10:00-09:00,12:00-14:30,16:00-18:00")); // false -> 10:00-09:00
        System.out.println(hasCorrectFormatAndRanges("09:00-10:00")); // true
        System.out.println(hasCorrectFormatAndRanges("09:00 10:00")); // false
        System.out.println(hasCorrectFormatAndRanges("09:00-10:00,09:00 10:00")); // false
        System.out.println(hasCorrectFormatAndRanges("09:00-10:00-12:00-14:30,16:00-18:00")); // false
        System.out.println(hasCorrectFormatAndRanges("09:00-10:00,12:00-14:30,16:00-18:00,")); // false
    }

    static boolean hasCorrectFormatAndRanges(String strTimeRanges) {
        if (!strTimeRanges.matches("(?:(?:\\d{2}:\\d{2}\\-\\d{2}:\\d{2})(?:,(?!$))?)*"))
            return false;
        String[] timeRanges = strTimeRanges.split(",");
        for (String timeRange : timeRanges) {
            String[] times = timeRange.split("-");
            try {
                if (LocalTime.parse(times[1]).isBefore(LocalTime.parse(times[0])))
                    return false;
            } catch (DateTimeParseException e) {
                return false;
            }
        }
        return true;
    }
}

Output:

true
false
false
true
false
false
false
false

Answer 2

You can use the following pattern for any given range of 2 times in the form of 24h clock:

private static final String HOURLY_TIME_PATTERN = "([01][0-9]|2[0-3]):([0-5][0-9])";
private static final String TIME_RANGER_PATTERN = HOURLY_TIME_PATTERN + "-" + HOURLY_TIME_PATTERN;
private static final String PATTERN = "^" + TIME_RANGER_PATTERN + "(," + TIME_RANGER_PATTERN + "?)*$";
private static final Pattern pattern = Pattern.compile(PATTERN);

public static void main(String[] args) {
    String input = "09:00-10:00,12:00-14:30,16:00-18:00";
    if (pattern.matcher(input).matches()) {
        System.out.println("We have a match!");
    }
}

Explanation:

• HOURLY_TIME_PATTERN is the pattern required for a single hour in a 24h format (e.g. 16:25)
• TIME_RANGER_PATTERN is the pattern to find a single time range (e.g. 16:25-22:50)
• PATTERN - is the pattern that ensure that we have at least 1 time range, and any other time range must be lead by a comma (we can have zero or more of them)