populating combobox from database

[kessy cruz]

Good morning, I'm trying to populate comboBox from database. its my first time and i'm messing it all up, i cant find a good tutorial about it online.
please help structure the code.Thanks you for taking time to read this.

<code>private void jComboBoxActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
try{
Connection conn = DriverManager.getConnection(DB_URL, DB_USERNAME, DB_PASSWORD);
Statement stst = (Statement)conn.createStatement();
String sql = "SELECT CodeId FROM Courses";
int index = 0;
ResultSet rs = stst.executeQuery(sql);
while(rs.next()){
// items[index]= rs.getString("CodeId");
// jComboBox.addItem(rs.getString("CodeId"));

//clears the contents of the combo box
Course course = new Course();
course.getCodeId();

jComboBox.removeAllItems();
jComboBox.insertItemAt("Course", 0);
jComboBox.setSelectedIndex(0);
// jComboBox.addItem(rs.getString(""));

for (int i = 1; i < course; i++){
jComboBox.insertItemAt(getCodeId[i], i);
}
}
rset.close();
stst.close();
}catch (SQLException e){
e.printStackTrace();
}
} </code>

[Fatih Keles]

Hi kessy,

Here is a sample code for you. What it does :
1) Creates a combobox
2) builds a model for combobox from items of type DemoModelItem (try commenting out overrided toString method)
3) sets combobox model

Make sure that you have visited "How to Use Combo Boxes" tutorial.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;

class DemoModelItem {
    public String objectName;
    public String objectType;
    
    public DemoModelItem(String objectName,String objectType){
        this.objectName = objectName;
        this.objectType = objectType;
    }
    
    public String toString(){
        return objectType+"-"+objectName;
    }
}

public class ComboTest {
    public static Connection getConnection() throws Exception {
        Connection conn = null;
        //open connection 
        return conn;
    }
    
    public static DefaultComboBoxModel buildComboBoxModel() throws Exception {
        DefaultComboBoxModel comboBoxModel = new DefaultComboBoxModel();
        String SQL = "SELECT object_name, object_type from some_table";        
        Connection c = null;
        try {
            c = getConnection();
            PreparedStatement ps = c.prepareStatement(SQL);
            ResultSet rs = ps.executeQuery();
            while(rs.next()){
                comboBoxModel.addElement(new DemoModelItem(rs.getString("OBJECT_NAME"),rs.getString("OBJECT_TYPE")));
            }
            rs.close();
            ps.close();
        } catch (Exception e) {
            throw e;
        }finally{
            try{c.close();}catch(Exception e){;}
        }
        return comboBoxModel;
    }

    public static void main(String[] args) throws Exception {
        JComboBox comboBox = new JComboBox();
        comboBox.setModel(buildComboBoxModel());

        JFrame frame = new JFrame("Combo Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.getContentPane().add(comboBox);
        frame.pack();
        frame.setVisible(true);
    }
}

[Neha Kaushik]

here instead of using
model.addElement() you should use JcomboBox.addItem();
thankyou..

[Jason Smit]

Fatih Keles wrote:Hi kessy,

Here is a sample code for you. What it does :
1) Creates a combobox
2) builds a model for combobox from items of type DemoModelItem (try commenting out overrided toString method)
3) sets combobox model

Make sure that you have visited "How to Use Combo Boxes" tutorial.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;

class DemoModelItem {
    public String objectName;
    public String objectType;
    
    public DemoModelItem(String objectName,String objectType){
        this.objectName = objectName;
        this.objectType = objectType;
    }
    
    public String toString(){
        return objectType+"-"+objectName;
    }
}

public class ComboTest {
    public static Connection getConnection() throws Exception {
        Connection conn = null;
        //open connection 
        return conn;
    }
    
    public static DefaultComboBoxModel buildComboBoxModel() throws Exception {
        DefaultComboBoxModel comboBoxModel = new DefaultComboBoxModel();
        String SQL = "SELECT object_name, object_type from some_table";        
        Connection c = null;
        try {
            c = getConnection();
            PreparedStatement ps = c.prepareStatement(SQL);
            ResultSet rs = ps.executeQuery();
            while(rs.next()){
                comboBoxModel.addElement(new DemoModelItem(rs.getString("OBJECT_NAME"),rs.getString("OBJECT_TYPE")));
            }
            rs.close();
            ps.close();
        } catch (Exception e) {
            throw e;
        }finally{
            try{c.close();}catch(Exception e){;}
        }
        return comboBoxModel;
    }

    public static void main(String[] args) throws Exception {
        JComboBox comboBox = new JComboBox();
        comboBox.setModel(buildComboBoxModel());

        JFrame frame = new JFrame("Combo Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.getContentPane().add(comboBox);
        frame.pack();
        frame.setVisible(true);
    }
}

I am getting an error on

c = getConnection();

using Netbeans:

cannot find symbol
symbol: method GetConnection()
location: variable conn of type Connection

Dereferencing null pointer 

[Dave Tolls]

That error mentions GetConnection.
The code shows a getConnection() method.

Java is case sensitive.

[Jason Smit]

Dave Tolls wrote:That error mentions GetConnection.
The code shows a getConnection() method.

Java is case sensitive.

I did change the name, but this is not the reason why I am getting the error. It would have mentioned that GetConnection did not exist.

Here is my method for the GetConnection method.

  public static Connection GetConnection() throws Exception
            {
                Connection conn = null;
                return conn;
            }

Below is the call to it.

c.GetConnection();

[Dave Tolls]

Jason Smit wrote:

Dave Tolls wrote:That error mentions GetConnection.
The code shows a getConnection() method.

Java is case sensitive.

I did change the name, but this is not the reason why I am getting the error. It would have mentioned that GetConnection did not exist.

It does:
cannot find symbol
symbol: method GetConnection()

Here is my method for the GetConnection method.

  public static Connection GetConnection() throws Exception
            {
                Connection conn = null;
                return conn;
            }

Below is the call to it.

c.GetConnection();

So is it compiling, because that bit I posted above says it wasn't compiling?

[Jason Smit]

I decided to create a class for this code.

Now I want to create an instance of the class, in another class which I have.

But I am struggling to set my ComboBox to the data.

e.g.

 SchemaJComboBox.setModel(SchemaComboBox.buildComboBoxModel()); 

---
What is the best way of calling the method to populate the data into my ComboBox which is in another class file?

[Jason Smit]

Hi,
I have managed to get this to work on my application.
It was more of changing some of the code to suit the application.
It is so far working. Thanks