Question

Here is my current program:

import java.applet.Applet;
import java.awt.Graphics;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

import javax.swing.JComboBox;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Timestamp;
import java.util.Properties;

public class CodesApplet extends Applet 
{
    private Properties properties;
    private String configFilePath;
    private FileInputStream fis;
    private String driverName;
    private String userName;
    private String password;
    private String url;

    private Connection conn;
    private Statement st;
    private Timestamp created = new Timestamp(System.currentTimeMillis());

    private JComboBox codes1;
    private JComboBox codes2;
    private JComboBox otherCodes;

    public void init() 
    {
        try 
        {
            //Loads the values from the properties file 
            try 
            {
                properties = new Properties();
                configFilePath="C:\\scriptProps.properties";
                fis = new FileInputStream(configFilePath);

                properties.load(fis);

                if (fis != null)
                {
                    fis.close();
                }
            } 
            catch (FileNotFoundException e) 
            {
                System.err.println("init(): FileNotFoundException(): " + e.getMessage());
            }

            driverName=properties.getProperty("driverName");
            userName=properties.getProperty("userName");
            password=properties.getProperty("password");
            url=properties.getProperty("url");

            //Establishes the connection to the database
            System.out.println("init(): loading OracleDriver for applet created at " + created.toString());
            Class.forName(driverName);
            System.out.println("init(): getting connection");
            conn = DriverManager.getConnection(url, userName, password);
            st = conn.createStatement();

            //Instantiates the previously declared variables for the drop-downs.
            codes1 = new JComboBox();
            codes2 = new JComboBox();
            otherCodes = new JComboBox();
        }
        catch (ClassNotFoundException e)
        {
            System.err.println("init(): ClassNotFoundException: " + e.getMessage());
        } 
        catch (SQLException e)
        {
            System.err.println("init(): SQLException: " + e.getMessage());
        } catch (IOException e) 
        {
            System.err.println("init(): IOException. " + e.getMessage());
        }
    }

    public void start() 
    {
        System.out.println("start(): ");
    }

    public void stop()
    {
        System.out.println("stop(): ");
    }

    //Returns the first drop-down...
    public JComboBox getComboBox1() 
    {
        codes1.removeAllItems();
        codes1.addItem("Please Select...");

        try 
        {
            ResultSet rs = st.executeQuery("select codes from myTable");

            while (rs.next()) 
            {
                codes1.addItem(rs.getString("codes"));
            }

            rs.close();
            st.close();
        } 
        catch (SQLException sqle)
        {
            System.out.println(sqle);
        }

        return codes1;
    }

    //Returns the second drop-down...
    public JComboBox getComboBox2() 
    {
        codes2.removeAllItems();
        codes2.addItem("Please Select...");

        try 
        {
            ResultSet rs = st.executeQuery("select codes from myTable");

            while (rs.next()) 
            {
                codes2.addItem(rs.getString("codes"));
            }

            rs.close();
            st.close();
        } 
        catch (SQLException sqle)
        {
            System.out.println(sqle);
        }

        return codes2;
    }

    //Returns the third drop-down...
    public JComboBox getComboBox3() 
    {
        otherCodes.removeAllItems();
        otherCodes.addItem("Please Select...");

        try 
        {
            ResultSet rs = st.executeQuery("select otherCodes from myTable2");

            while (rs.next()) 
            {
                otherCodes.addItem(rs.getString("otherCodes"));
            }

            rs.close();
            st.close();
        } 
        catch (SQLException sqle)
        {
            System.out.println(sqle);
        }

        return otherCodes;
    }

    public void paint(Graphics g)
    {
        System.out.println("paint(): creating the drop-downs...");

        getComboBox1();
        getComboBox2();
        getComboBox3();
    }

    public void destroy() 
    {
        System.out.println("destroy(): closing connection for applet created at " + created.toString());

        try 
        {
            conn.close();
        } 
        catch (SQLException e) 
        {
            System.err.println("destroy: SQLException: " + e.getMessage());
        }
    }
}

Essentially, what I want to do is have this applet that pulls data from multiple tables and populates drop-down boxes with that data. I’ve seen some examples on how to do this with one drop-down (thus why you see one return statement involving codes1).

My primary questions are:

• In general, am I doing this right? Is this the best way to pull in multiple fields from multiple tables?
• Also, I understand that this would only populate the combo boxes. If I wanted to allow the user to hit a button after selecting the appropriate values from the drop-downs (after they’ve been populated), and store those values to a separate table in the database, how would I do that?

Answer 1

There are many problems in your applet:

• You never add your comboboxes to a top-level container hierarchy
• You can add ActionListener to the JComboBoxes if you want to be notified of user selection changes
• You should not override paint
• You are recreating the content of your comboboxes everytime paint is called. You should rather create and add your comboboxes upon applet initalization
• Applet are usually distributed through web pages/server: your propery file won’t be available
• Unless your database allow remote access, this will not work.
• To add a button to the display, simply call new JButton(“My button”) and add it to the component hierarchy
• …

Here is a link to Swing tutorials. I think that many chapters can help you