Need to create only one object

[Yohan Weerasinghe]

Hello all,

Please have a look at the following set of codes

MyPhoneBookMain.java

import javax.swing.*;


public class MyPhoneBookMain
{
    public static void main(String[]args)
    {
        try
        {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
            
            new MainView();
        }
        catch(Exception e)
        {
            JOptionPane.showMessageDialog(null, "GUI Error");
            e.printStackTrace();
        }
    }
}

MainView.java

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;

public class MainView extends JFrame
{
    private JPanel centerPanel;
    
    private EditBean eb = new EditBean();
    private DatabaseContactable dbc;
    
    public MainView()
    {
     
        centerPanel = new JPanel();
        centerPanel.add(eb);
        
       
        getContentPane().add(centerPanel,"Center");
        getContentPane().add(new JPanel(),"East");
        getContentPane().add(new JPanel(),"South");
        
        
        //Creating the Connection
        dbc = new DatabaseHandler();

        
        //Setting Defaults
        this.addWindowListener(new WindowClosingAction());
        this.setSize(700,400);
        this.validate();
        this.setVisible(true);
        this.pack();
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     
    }
    
    private class WindowClosingAction extends WindowAdapter
    {
        public void windowClosing(WindowEvent we)
        {
            dbc.closeConnection();;
        }
    }
    
}

EditButtonOptions

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import java.sql.*;

public class EditButtonOptions extends JPanel
{
    private JButton go;
    private EditBean edit;
    private DatabaseContactable dbc;
    
    public EditButtonOptions()
    {
        
       dbc = new DatabaseHandler();      
        
        go = new JButton("Go");
        go.addActionListener(new ButtonAction()); 
    
        this.add(go);
        
    }
    
    public void setEditBean(EditBean edit)
    {
        this.edit = edit;
    }
    
 
    
    private class ButtonAction implements ActionListener
    {
        public void actionPerformed(ActionEvent ae)
        {
                    String message = dbc.insertData("Yohan", "weerasinghe");
                    JOptionPane.showMessageDialog(null, message);
                
            
        }
    }
    
   
}

EditBean.java

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;

public class EditBean extends JPanel implements java.io.Serializable
{
    private JLabel firstName;
    
    protected JScrollPane scroll;
    
    private JPanel mainPanel, centerPanel, southPanel;
    
    private GridBagLayout gbl;
    private GridBagConstraints gbc;
    
    private boolean correct;
        private EditButtonOptions eb;
    
    public EditBean()
    {
        eb = new EditButtonOptions();
        //Declaring Instance Variables
        
        gbl = new GridBagLayout();
        gbc = new GridBagConstraints();
        
        firstName = new JLabel("First Name: ");
       
        
        
        //Creating the GUI
        
        centerPanel = new JPanel();
        centerPanel.setLayout(gbl);
        
        gbc.gridx = 1;
        gbc.gridy = 1;
        gbc.fill = GridBagConstraints.BOTH;
        gbc.insets = new Insets(2,2,2,2);
        centerPanel.add(firstName,gbc);
        
       
        
        
     
        this.setLayout(new BorderLayout());
        this.add(centerPanel,"Center");
        this.add(eb,"South");
        this.setSize(400, 400);     
        eb.setEditBean(this);
    }
}
 

DatabaseHandler.java

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import java.sql.*;

public class DatabaseHandler implements DatabaseContactable
{

    public DatabaseHandler()
    {
        try
        {
                     
            System.out.println("Connection Created");
        }
        catch(Exception e)
        {
           e.printStackTrace();
        }
    }


    @Override
    public void closeConnection()
    {
        try
        {
            System.out.println("Connection Closed");
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }

    @Override
    public String insertData(String firstNameTxt, String lastNameTxt) 
    {
        String message = "";
        int result=0;

           
        return message;
    }
    
}

DatabaseContactable.java

public interface DatabaseContactable
{

    public void closeConnection();
    public String insertData(String firstNameTxt, String lastNameTxt);
}

When I run the program and click the "go" button, this is what I get

Connection Created
Connection Created
Connection Closed

As you can see here, it is creating 2 DatabaseHandler objects. MainView.java is creating one object and EditButtonOptions.java created another object. This is a JDBC application, so that means this is definitely creating 2 connections, and only closing one when the program exited, which is definitely not good. So, I need to create only one object, but need to use that in both MainView.java and EditButtonOptions.java files. What I tried is making the constructor of DatabaseHandler.java file "private" but you know, then I lose the access ( I found a way to access private constructors in http://www.java-forums.org/new-java/12221-accessing-private-constructor.html, but since the author says it is a HACKING method, I don't think it is a professional way). How can I create only one object, and use it in any place without any issue? Please help..

[Jayesh A Lalwani]

Several ways you can do this:-

a) You could have MainView create a DatabaseHandler, give the reference to it to EditBean and EditBean can give it to EditButtonOptions.
b) You could use a singleton pattern
c) You can use dependency injection pattern. Here a factory creates all objects, and when object A and B needs C, the factory creates instance of A, B and C and gives the instance of C to A and B

[Yohan Weerasinghe]

Jayesh A Lalwani wrote:Several ways you can do this:-

a) You could have MainView create a DatabaseHandler, give the reference to it to EditBean and EditBean can give it to EditButtonOptions.
b) You could use a singleton pattern
c) You can use dependency injection pattern. Here a factory creates all objects, and when object A and B needs C, the factory creates instance of A, B and C and gives the instance of C to A and B

Thanks a lot for the reply Jayesh. I will check this tomorrow and let you know the result

[Yohan Weerasinghe]

Sorry for the delay Jayesh. I had some issues with my computer.

I used the first method you have mentioned. It worked!! Thanks a lot for helping me, I really appreciate it