Program: How to validate date format using regular expression in java?

The below given example shows how to validate date format using regular expression. This example checks for dd/mm/yyyy date format.

package com.java2novice.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class MyDateFormat {

	private static Pattern dateFrmtPtrn = 
			Pattern.compile("(0?[1-9]|[12][0-9]|3[01])/(0?[1-9]|1[012])/((19|20)\\d\\d)");
	
	public static boolean validateDateFormat(String userName){
		
		Matcher mtch = dateFrmtPtrn.matcher(userName);
		if(mtch.matches()){
			return true;
		}
		return false;
	}
	
	public static void main(String a[]){
		System.out.println("Is '03/04/2012' a valid date format? "
						+validateDateFormat("03/04/2012"));
		System.out.println("Is '12/23/2012' a valid date format? "
						+validateDateFormat("12/23/2012"));
		System.out.println("Is '12/12/12' a valid date format? "
						+validateDateFormat("12/12/12"));
		System.out.println("Is '3/4/2012' a valid date format? "
						+validateDateFormat("3/4/2012"));
	}
}

Is '03/04/2012' a valid date format? true
Is '12/23/2012' a valid date format? false
Is '12/12/12' a valid date format? false
Is '3/4/2012' a valid date format? true