hello all. I need some help. I have wrote this code and dont now how to sort surnames in alphabet from my file to other file.

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

class Asmuo { String pavarde; String vardas; long buvLaikas; int atv1; int atv2; int atv3; }

class Irasas { Asmuo duom; Irasas kitas; }

class Sarasas { private Irasas p;

Sarasas() {
    p = null;
}

Irasas itrauktiElementa(String pv, String v, long laikas, int d0, int d1,
        int d2) {
    String pvrd, vrd;
    int data0;
    int data1;
    int data2;
    long lks;
    lks = laikas;
    pvrd = pv;
    vrd = v;
    data0 = d0;

    data1 = d1;

    data2 = d2;
    Irasas r = new Irasas();
    r.duom = new Asmuo();
    uzpildymasDuomenimis(r, pvrd, vrd, lks, d0, d1, d2);
    r.kitas = p;
    p = r;
    return r;
}

void uzpildymasDuomenimis(Irasas r, String pv, String v, long laik, int d0,
        int d1, int d2) {
    r.duom.pavarde = pv;
    r.duom.vardas = v;
    r.duom.atv1 = d0;
    r.duom.buvLaikas = laik;
    r.duom.atv2 = d1;
    r.duom.atv3 = d2;
}

void spausdinti() {
    Irasas d = p;
    int i = 0;
    try {
        FileWriter fstream = new FileWriter("rez.txt");
        BufferedWriter rez = new BufferedWriter(fstream);
        while (d != null) {
            System.out.println(d.duom.pavarde + " " + d.duom.vardas + " "
                    + d.duom.buvLaikas + " " + d.duom.atv1 + " "
                    + d.duom.atv2 + " " + d.duom.atv3);
            rez.write(d.duom.pavarde + " " + d.duom.vardas + " "
                    + d.duom.buvLaikas + " " + d.duom.atv1 + " "
                    + d.duom.atv2 + " " + d.duom.atv3 + "\n");
            d = d.kitas;
            i++;
        }
        rez.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }

}

}

public class Gyventojai {

public static void main(String args[]) {
    Sarasas sar = new Sarasas();
    Calendar atv = Calendar.getInstance();
    Calendar isv = Calendar.getInstance();

    try {
        FileInputStream fstream = new FileInputStream("duom.txt");
        DataInputStream in = new DataInputStream(fstream);
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
        String eil;
        while ((eil = br.readLine()) != null) {
            String[] cells = eil.split(" ");
            String pvrd = cells[0];
            String vrd = cells[1];
            atv.set(Integer.parseInt(cells[2]), Integer.parseInt(cells[3]),
                    Integer.parseInt(cells[4]));
            isv.set(Integer.parseInt(cells[5]), Integer.parseInt(cells[6]),
                    Integer.parseInt(cells[7]));
            long laik = (isv.getTimeInMillis() - atv.getTimeInMillis())
                    / (24 * 60 * 60 * 1000);
            int d0 = Integer.parseInt(cells[2]);
            int d1 = Integer.parseInt(cells[3]);
            int d2 = Integer.parseInt(cells[4]);
            sar.itrauktiElementa(pvrd, vrd, laik, d0, d1, d2);

        }
        in.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }

    sar.spausdinti();

}

}