Как найти файлы только с определенным расширением

package com.example.io;

import java.io.*;

public class FindCertainExtension {

    private static final String FILE_DIR = "c:\\folder";
    private static final String FILE_TEXT_EXT = ".jpg";

    public static void main(String args[]) {
        new FindCertainExtension().listFile(FILE_DIR, FILE_TEXT_EXT);
    }

    public void listFile(String folder, String ext) {

        GenericExtFilter filter = new GenericExtFilter(ext);

        File dir = new File(folder);

        if(dir.isDirectory()==false){
            System.out.println("Directory does not exists : " + FILE_DIR);
            return;
        }

        // list out all the file name and filter by the extension
        String[] list = dir.list(filter);

        if (list.length == 0) {
            System.out.println("no files end with : " + ext);
            return;
        }

        for (String file : list) {
            String temp = new StringBuffer(FILE_DIR).append(File.separator)
                    .append(file).toString();
            System.out.println("file : " + temp);
        }
    }

    // inner class, generic extension filter
    public class GenericExtFilter implements FilenameFilter {

        private String ext;

        public GenericExtFilter(String ext) {
            this.ext = ext;
        }

        public boolean accept(File dir, String name) {
            return (name.endsWith(ext));
        }
    }
}