simple JDBC --> can't get started

I have a simple test.java which tries to connect to a database I have
created, my user name is "yangsu" which is created by "createuser yangsu"
My db_hba.conf has only the following lines:

local        all                                         trust
host         all         127.0.0.1     255.255.255.255   trust
host         all         129.186.68.160  255.255.255.255 trust

My machine name is inkle.cs.iastate.edu(ip 129.186.68.160), my execution
of "java test" yields:

Class.forName OK!
java.sql.SQLException: Connection failed: java.net.ConnectException: Connection refused

What is the error?(what causes the error?) Thanks for any suggestions.

yang
http://www.cs.iastate.edu/~yangsu/


Following is the test.java:

import java.io.*;
import java.net.*;
import java.sql.*;

public class test{

   public static void main(String args[]){
        try{
                Class.forName("postgresql.Driver");
                System.out.println("Class.forName OK!");

                String url="jdbc:postgresql://inkle.cs.iastate.edu/test";
                String usr="yangsu";
                String pwd="";

                Connection db = DriverManager.getConnection(url, usr, pwd);
                if(db != null){
                        System.out.println("Connected to db");
                }else{
                        System.out.println("Can't connect to db");
                }

                Statement st = db.createStatement();
                ResultSet rs = st.executeQuery("select * from classmate");

                while(rs.next()){
                        System.out.println(rs.getString("name"));
                        System.out.println(rs.getBoolean("sex"));
                        System.out.println(rs.getInt("age"));
                }
        }catch(Exception e){
                System.out.println(e.toString());
        }
   }

}