Mine

import java.io.*;
import java.util.*;

public class getFiles implements FilenameFilter {
	String str = "";

	public getFiles(String s) {
		str = s;
	}

	// Override default accept method, which checks if a file should be included in the list
	public boolean accept(File f, String s) {
		return s.toLowerCase().endsWith(str.toLowerCase());
	}

	public static void main(String[] args) throws IOException {
		Scanner stdin = new Scanner(System.in);
		File f = new File(".");
		String ext = "";

		// Ask user for the file extension and set it into a String variable
		System.out.println("Enter the file extension: ");
		ext = stdin.next();

		getFiles gf = new getFiles(ext);
		String strarr[] = f.list(gf);

		// Files were found
		if (strarr.length > 1) {
			// Shuffle the array into a random order
			Collections.shuffle(Arrays.asList(strarr));

			try {
				// File to write to
				PrintWriter pw = new PrintWriter(new FileWriter("list.txt"));

				// Loop through the array and write each entry to the file
				for (int i = 1; i <= strarr.length-1; i++)
					pw.println(strarr[i].substring(0,strarr[i].length()-(ext.length()+1)));

				// Close the file
				pw.close();	
			}
			catch (IOException i) {
				i.printStackTrace();
			}
		}

		// No files were found
		else {
			System.out.println("No files found with extension " + ext);
			return;
		}
	}
}