Para utilizar a função HASH MD(5)

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5 {

    private static MessageDigest md = null;

    static {
        try {
            md = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException ex) {
            ex.printStackTrace();
        }
    }

    private static char[] hexCodes(byte[] text) {
        char[] hexOutput = new char[text.length * 2];
        String hexString;

        for (int i = 0; i < text.length; i++) {
            hexString = "00" + Integer.toHexString(text[i]);
            hexString.getChars(hexString.length() - 2,
                    hexString.length(), hexOutput, i * 2);
        }

        return hexOutput;
    }

    public static String generate(String pwd) {
        if (md != null) {
            return new String(hexCodes(md.digest(pwd.getBytes())));
        }
        return null;
    }
}

Md5.generate("sua string");

import java.util.*;
import java.io.*;
import java.security.*;

class TesteMD5 {
    private static String hexString (byte[] bytes) {
        Formatter fm = new Formatter (new StringBuilder());
        for (int i = 0; i < bytes.length; ++i) {
            fm.format ("%02X", bytes[i] & 0xFF);
        }
        return fm.toString();
    }
    public static String calcMD5 (String str) {
        try {
            byte[] bytes = str.getBytes ("UTF-8");
            MessageDigest md = MessageDigest.getInstance ("MD5");
            return hexString (md.digest (bytes));
        } catch (UnsupportedEncodingException ex) {
            // UTF-8 sempre está disponível
            throw new RuntimeException ("Can't happen", ex);
        } catch (NoSuchAlgorithmException ex) {
            // MD5 sempre está disponível
            throw new RuntimeException ("Can't happen", ex);
        }
    }
    public static void main (String[] args) {
        System.out.println (calcMD5 ("Jose Aparecido"));
    }
}