Connection URL or username or password errors!
org.postgresql.util.PSQLException: ResultSet not positione properly, perhaps you need to call next.
at  org.postgresql.jdbc2.AbstractJdbc2ResultSet.checkResultSet(AbstractJdbc2ResultSet.java:2926)
at org.postgresql.jdbc2.AbstractJdbc2ResultSet.getString(AbstractJdbc2ResultSet.java:2001)
at org.postgresql.jdbc2.AbstractJdbc2ResultSet.getString(AbstractJdbc2ResultSet.java:2613)
at HW2_report3.main(HW2_report3.java:59)

public static void main(String[] args)
{
    String usr ="zihengma";
    String pwd ="Maziheng1993";
    String url ="jdbc:postgresql://localhost:5432/postgres";

    try
    {
        Class.forName("org.postgresql.Driver");
        System.out.println("Success loading Driver!");
    }

    catch(Exception e)
    {
        System.out.println("Fail loading Driver!");
        e.printStackTrace();
    }

    try
    {
        // connect once, and create the first hashmap.

        Connection conn = DriverManager.getConnection(url, usr, pwd);
        System.out.println("Success connecting server!");

        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("SELECT * FROM Sales");
        HashMap<String, ArrayList<Integer>> hashMap = new HashMap<String, ArrayList<Integer>>();

        while (rs.next()){
            String string = rs.getString("cust") + " " + rs.getString("prod");
            if (hashMap.containsKey(string)) {
                hashMap.get(string).set(0,hashMap.get(string).get(0) + Integer.parseInt(rs.getString("quant"))/3);
            }
            else{
                ArrayList<Integer> arrayList = new ArrayList<Integer>();
                arrayList.add(Integer.parseInt(rs.getString("quant"))/3);
                hashMap.put(string, arrayList);
            }
        }

        // connect second time, and create the second hashmap1
        //which can use the data in the first hashmap.
        Connection conn1 = DriverManager.getConnection(url, usr, pwd);
        System.out.println("Success connecting server!");
        Statement stmt1 = conn1.createStatement();
        ResultSet rs1 = stmt1.executeQuery("SELECT * FROM Sales");

        HashMap<String, ArrayList<Integer>> hashMap1 = new HashMap<String, ArrayList<Integer>>();
        while (rs1.next()){
            ArrayList<Integer> arrayList1 = new ArrayList<Integer>();
            String string1 = rs.getString("cust") + " " + rs.getString("prod");
            if (hashMap1.containsKey(string1)) {
                hashMap1.get(string1).set(0,hashMap1.get(string1).get(0) + Integer.parseInt(rs1.getString("quant")));
                if(arrayList1.get(0) == hashMap.get(string1).get(0)){
                    arrayList1.set(1,Integer.parseInt(rs1.getString("month")));
                }
            }
            else{

                arrayList1.add(Integer.parseInt(rs1.getString("quant")));
                arrayList1.add(0);
                if(arrayList1.get(0) == hashMap.get(string1).get(0)){
                    arrayList1.set(1,Integer.parseInt(rs1.getString("month")));
                }
                hashMap1.put(string1, arrayList1);
            }
        }

        System.out.printf("%-11s", "CUSTOMER");
        System.out.printf("%-11s", "PRODUCT");
        System.out.printf("%-11s", "1/3TOTAL");
        System.out.println();
        System.out.printf("%-11s", "========");
        System.out.printf("%-11s", "========");
        System.out.printf("%-11s", "========");
        System.out.println();
        Set<String> set = hashMap.keySet();
        for (String s: set) {
            String[] strings = s.split(" ");
            System.out.printf("%-11s", strings[0]);
            System.out.printf("%-11s", strings[1]);
            System.out.printf("%-11s", hashMap.get(s).get(0));
            System.out.println();
        }

        System.out.printf("%-11s", "CUSTOMER");
        System.out.printf("%-11s", "PRODUCT");
        System.out.printf("%-11s", "1/3Month");
        System.out.println();
        System.out.printf("%-11s", "========");
        System.out.printf("%-11s", "========");
        System.out.printf("%-11s", "========");
        System.out.println();
        Set<String> set1 = hashMap.keySet();
        for (String s: set1) {
            String[] strings = s.split(" ");
            System.out.printf("%-11s", strings[0]);
            System.out.printf("%-11s", strings[1]);
            System.out.printf("%-11s", hashMap1.get(s).get(1));
            System.out.println();
        }


    }catch(SQLException e)
    {
        System.out.println("Connection URL or username or password errors!");
        e.printStackTrace();
    }
}