Connecting to SQL Server 2008 from Java

I am trying to connect to SQL Server 2008 server from Java

here is a program

import java.sql.*;

public class connectURL {

    public static void main(String[] args) {

        // Create a variable for the connection string.
        String connectionUrl = "jdbc:sqlserver://localhost/SQLEXPRESS/Databases/HelloWorld:1433;";// +

        // Declare the JDBC objects.
        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;

            try {
                // Establish the connection.
                    con = DriverManager.getConnection(connectionUrl);

                    // Create and execute an SQL statement that returns some data.
                    String SQL = "SELECT TOP 10 * FROM Person.Contact";
                    stmt = con.createStatement();
                    rs = stmt.executeQuery(SQL);

                    // Iterate through the data in the result set and display it.
                    while ( {
                        System.out.println(rs.getString(4) + " " + rs.getString(6));

        // Handle any errors that may have occurred.
        catch (Exception e) {

        finally {
            if (rs != null) try { rs.close(); } catch(Exception e) {}
                if (stmt != null) try { stmt.close(); } catch(Exception e) {}
                if (con != null) try { con.close(); } catch(Exception e) {}

But it shows error as The TCP/IP connection to the host localhost/SQLEXPRESS/Databases/HelloWorld, port 1433 has failed. Error: "null. Verify the connection properties, check that an instance of SQL Server is running on the host and accepting TCP/IP connections at the port, and that no firewall is blocking TCP connections to the port.".
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at connectURL.main(

I have given followed all the instructions as given in

What can be the problem ?