public class Main {

    public static void main(String[] args) throws Exception {

        String xml =
                "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                        "<folder name=\"c\">\n" +
                        "    <folder name=\"program files\">\n" +
                        "        <folder name=\"uninstall information\"> \n" +
                        "                <folder name=\"temporal\" />\n" +
                        "                <folder name=\"foo\" />\n" +
                        "                <folder name=\"uninstall information\"> \n" +
                        "                    <folder name=\"temporal\" />\n" +
                        "                    <folder name=\"foo\" />\n" +
                        "                    <folder name=\"uninstall information\"> \n" +
                        "                        <folder name=\"temporal\" />\n" +
                        "                        <folder name=\"foo\" />\n" +
                        "                        <folder name=\"uninstall information\"> \n" +
                        "                             <folder name=\"temporal\" />\n" +
                        "                             <folder name=\"foo\" />\n" +
                        "                        </folder>\n" +
                        "                    </folder>\n" +
                        "                </folder>\n" +
                        "        </folder>\n" +
                        "    </folder>\n" +
                        "    <folder name=\"fusers\" />\n" +
                        "</folder>";

        Collection<String> filter = folderNames(xml, 'f');
        filter.forEach(System.out::println);


    }

    public static Collection<String> folderNames(String xml, char startingLetter) throws Exception {
        String fstPattern = "<folder name=\"";
        List<String> results = new ArrayList<>();

        String[] patterns = xml.split(">");
        for (String p : patterns) {
            int indexof = p.indexOf("=") + 2;
            if (p.contains(fstPattern) && indexof >= 0) {
                int endIndexOF = p.lastIndexOf("\"");
                String result = p.substring(indexof, endIndexOF);
                if(result.charAt(0)==startingLetter){
                    results.add(result);
                }
            }
        }
        return results;
    }


}