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java regex pattern validate 12 hours format


Regular expressions

Regular expressions represents a sequence of symbols and characters expressing a string or pattern to be searched for within a longer piece of text. The abbreviation for regular expression is regex. In programming regular expressions are mainly used to define constraint on strings like password, email validation.

(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)

This regular expression refers to a pattern which start from 0-12, then a semi colon (:) and follow by 00-59, and end with am or pm.

Example

package com.tutorialspointexamples;
 
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class RegexTest {
	private static final String PATTERN = 
			"(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)";
	public static void main(String args[]){ 
		List<String> values = new ArrayList<String>();	
		values.add("3:00 am"); 
		values.add("5:00 PM"); 
		values.add("23:00 am");
		values.add("01:00 pm");
 
		Pattern pattern = Pattern.compile(PATTERN);
		for (String value : values){
		  Matcher matcher = pattern.matcher(value);
		  if(matcher.matches()){
			  System.out.println("Time "+ value +" is valid 12Hours Format");
		  }else{
			  System.out.println("Time "+ value +" is invalid 12Hours Format");
		  }		  
		}
	}
}

Output

Time 3:00 am is valid 12Hours Format
Time 5:00 PM is valid 12Hours Format
Time 23:00 am is invalid 12Hours Format
Time 01:00 pm is invalid 12Hours Format
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