Program: How to validate file extensions using regular expression in java?

The below given example shows how to validate a file extensions using regular expression. The regular expression allows txt, doc, csv, and pdf file extensions only.

package com.java2novice.regex;

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

public class MyFileExtenValidation {

private static Pattern fileExtnPtrn = Pattern.compile("([^\\s]+(\\.(?i)(txt|doc|csv|pdf))$)");
	
	public static boolean validateFileExtn(String userName){
		
		Matcher mtch = fileExtnPtrn.matcher(userName);
		if(mtch.matches()){
			return true;
		}
		return false;
	}
	
	public static void main(String a[]){
		System.out.println("Is 'java2novice.pdf' allowed file? "
						+validateFileExtn("java2novice.pdf"));
		System.out.println("Is 'cric.doc' allowed file? "
						+validateFileExtn("cric.doc"));
		System.out.println("Is 'java.gif' allowed file? "
						+validateFileExtn("java.gif"));
		System.out.println("Is 'novice.mp3' allowed file? "
						+validateFileExtn("novice.mp3"));
		System.out.println("Is 'java_2.jpeg' allowed file? "
						+validateFileExtn("java_2.jpeg"));
	}
}

Is 'java2novice.pdf' allowed file? true
Is 'cric.doc' allowed file? true
Is 'java.gif' allowed file? false
Is 'novice.mp3' allowed file? false
Is 'java_2.jpeg' allowed file? false