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About Nikos Maravitsas

Nikos Maravitsas
Nikos has graduated from the Department of Informatics and Telecommunications of The National and Kapodistrian University of Athens. During his studies he discovered his interests about software development and he has successfully completed numerous assignments in a variety of fields. Currently, his main interests are system’s security, parallel systems, artificial intelligence, operating systems, system programming, telecommunications, web applications, human – machine interaction and mobile development.

Validate Time In 24 Hours Format with Java Regular Expression example

In this tutorial we are going to see how to validate 24 Hours time format with Java Regular Expressions.The basic policy about the 24 hours format is that:

  • It should start with two digits from 00 to 23.
  • It must be followed by ‘:’.
  • It should be followed by two digits from 00 to 59.

So this is the regular expression we are going to use for 12 hours format validation:


You can take a look at the Pattern class documentation to learn how to construct your own regular expressions according to your policy.

1. Validator class

This is the class that we are going to use for 24 hours time format validation.


package com.javacodegeeks.java.core;

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Time24hFormatValidator{
	private Pattern pattern;
	  private Matcher matcher;

	  private static final String TIME12HOURS_PATTERN = "([01]?[0-9]|2[0-3]):[0-5][0-9]";

	  public Time24hFormatValidator(){
		  pattern = Pattern.compile(TIME12HOURS_PATTERN);

	  public boolean validate(final String time){		  
		  matcher = pattern.matcher(time);
		  return matcher.matches();	    	    

2. Unit Testing our Time24hFormatValidator class

For unit testing we are going to use JUnit. Unit testing is very important in these situations because they provide good feedback about the correctness of our regular expressions. You can test your program and reassure that your regular expression meets the rules on your policy about the form of 24 hour time format.

This is a basic test class:


package com.javacodegeeks.java.core;

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.Collection;

import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;

public class Time24hFormatValidatorTest {

	private String arg;
	private static Time24hFormatValidator time24hFormatValidator;
	private Boolean expectedValidation;

	public Time24hFormatValidatorTest(String str, Boolean expectedValidation) {
		this.arg = str;
		this.expectedValidation = expectedValidation;

	public static void initialize() {
		time24hFormatValidator = new Time24hFormatValidator();

	public static Collection<Object[]> data() {
		Object[][] data = new Object[][] {
				{ "10:00 am", false }, // there should be no am|pm
				{ "2.20" , false },    // wrong format
				{ "1 10", false },     // wrong format
				{ "24:20", false },    // out of range
				{ "09:35", true },                         
				{ "7:30", true },
				{ "23:30", true } };
		return Arrays.asList(data);
	public void test() {
		Boolean res = time24hFormatValidator.validate(this.arg);
		String validv = (res) ? "valid" : "invalid";
		System.out.println("Time Format "+arg+ " is " + validv);
		assertEquals("Result", this.expectedValidation, res);




Time Format 10:00 am is invalid
Time Format 2.20 is invalid
Time Format 1 10 is invalid
Time Format 24:20 is invalid
Time Format 09:35 is valid
Time Format 7:30 is valid
Time Format 23:30 is valid

This was an exampl on how to validate time in 24 Hours format with Java Regular Expression.

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