Regular expressions are a powerful tool used for pattern matching in strings. If you’re working with time-related data in Java, you may need to match specific time patterns such as 12-hour or 24-hour time format. In this blog post, we’ll explore how to use Java regular expressions to match these time patterns.

12-Hour Time Format Matching

To match a time in the 12-hour format (hh:mm AM/PM), you can use the following regular expression:

String regex = "^(0?[1-9]|1[0-2]):[0-5][0-9] (AM|PM)$";

Let’s break down the regular expression:

• ^ and $ - The caret (^) and dollar sign ($) are anchors that ensure the entire string matches the pattern.
• (0?[1-9]|1[0-2]) - This part matches the hours. It allows for either a single digit (0-9) or a two-digit number starting with 1 or 2.
• : - Matches the colon character used to separate hours and minutes.
• [0-5][0-9] - Matches the minutes. It ensures that minutes are in the range of 00-59.
• (AM|PM) - Matches either “AM” or “PM” for the time period.

Here’s an example of how to use the regular expression to match a time string:

String time = "08:30 AM";
boolean isMatch = time.matches(regex);
System.out.println("Is it a valid time in 12-hour format? " + isMatch);

24-Hour Time Format Matching

To match a time in the 24-hour format (hh:mm), you can use the following regular expression:

String regex = "^([01]?[0-9]|2[0-3]):[0-5][0-9]$";

Breaking down the regular expression:

• ([01]?[0-9]|2[0-3]) - Matches the hours. It allows for either a single digit (0-9) or a two-digit number starting with 0, 1, or 2.
• : - Matches the colon character used to separate hours and minutes.
• [0-5][0-9] - Matches the minutes. It ensures that minutes are in the range of 00-59.

Here’s an example of using the regular expression to match a time string:

String time = "17:45";
boolean isMatch = time.matches(regex);
System.out.println("Is it a valid time in 24-hour format? " + isMatch);

Conclusion

Java regular expressions provide a flexible way to match specific time patterns. By using the appropriate regular expressions, you can validate whether a given string matches the desired time format, whether it’s in 12-hour or 24-hour format. This can be useful when working with time-related data in Java applications.

#Java #RegularExpressions