Implement a function FolderNames, which accepts a string containing an XML file that specifies folder structure and returns all folder names that start with startingLetter.

Folders.Java

package javaproblems;

import java.io.StringReader;
import java.util.ArrayList;
import java.util.Collection;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;

public class Folders {

    public static Collection<String> folderNames(String xml, char startingLetter) throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        InputSource is = new InputSource(new StringReader(xml));
        Document doc = builder.parse(is);
        NodeList node = doc.getElementsByTagName("folder");
        Collection<String> result = new ArrayList<String>();
        for (int i = 0; i < node.getLength(); i++) {
            String nodeName = node.item(i).getAttributes().getNamedItem("name").getNodeValue();
            if (nodeName.toCharArray()[0] == startingLetter) {
                result.add(nodeName);
            }
        }
        return result;
    }

    public static void main(String[] args) throws Exception {
        String xml
                = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
                + "<folder name=\"c\">"
                + "<folder name=\"program files\">"
                + "<folder name=\"uninstall information\" />"
                + "</folder>"
                + "<folder name=\"users\" />"
                + "</folder>";

        Collection<String> names = folderNames(xml, 'u');
        for (String name : names) {
            System.out.println(name);
        }
    }
}