sorting elements from xml file in java

i want to sort elements in xml file according to chosen algorithm type by user in java.i have merged xml file which contains 10 xml files. so it will be like first user select type of algorithm and then program sort elements as user wants.how can i do this? pls help me

here is how i merged xml files

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;

public class Merge2 {

public static void main(String[] args) {
    String sourceFile1Path = "C:\\Users\\project\\Numbers1.xml";
    String sourceFile2Path = "C:\\Users\\project\\Numbers2.xml";
    String sourceFile3Path = "C:\\Users\\project\\Numbers3.xml";
    String sourceFile4Path = "C:\\Users\\project\\Numbers4.xml";
    String sourceFile5Path = "C:\\Users\\project\\Numbers5.xml";
    String sourceFile6Path = "C:\\Users\\project\\Numbers6.xml";
    String sourceFile7Path = "C:\\Users\\project\\Numbers7.xml";
    String sourceFile8Path = "C:\\Users\\project\\Numbers8.xml";
    String sourceFile9Path = "C:\\Users\\project\\Numbers9.xml";
    String sourceFile10Path = "C:\\Users\\project\\Numbers10.xml";

    String mergedFilePath = "C:\\Users\\project\\mergedXML.xml";

    File[] files = new File[10];
    files[0] = new File(sourceFile1Path);
    files[1] = new File(sourceFile2Path);
    files[2] = new File(sourceFile3Path);
    files[3] = new File(sourceFile4Path);
    files[4] = new File(sourceFile5Path);
    files[5] = new File(sourceFile6Path);
    files[6] = new File(sourceFile7Path);
    files[7] = new File(sourceFile8Path);
    files[8] = new File(sourceFile9Path);
    files[9] = new File(sourceFile10Path);


    File mergedFile = new File(mergedFilePath);

    mergeFiles(files, mergedFile);
}
public static void mergeFiles(File[] files, File mergedFile) {

    FileWriter fstream = null;
    BufferedWriter out = null;
    try {
        fstream = new FileWriter(mergedFile, true);
         out = new BufferedWriter(fstream);
    } catch (IOException e1) {
        e1.printStackTrace();
    }

    for (File f : files) {
        System.out.println("merging: " + f.getName());
        FileInputStream fis;
        try {
            fis = new FileInputStream(f);
            BufferedReader in = new BufferedReader(new InputStreamReader(fis));

            String aLine;
            while ((aLine = in.readLine()) != null) {
                out.write(aLine);
                out.newLine();
            }

            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    try {
        out.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

}

and my merged xml file starts like below

<numberList>
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<number index="1">770820</number>
<number index="2">640903</number>
<number index="3">997132</number>
<number index="4">193504</number>   

i want to show it like

 <numberList>
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<number index="1">193504</number>
<number index="2">640903</number>
<number index="3">770820</number>
<number index="4">997132</number>