How do you know when another class has been updated?

I am writing a Java program that displays a combo box that gets information from a properties file. There is a customization class that will allow the user to update the names of the fields that are in the combo box. My problem is when the settings class is called and modified, I cannot figure out how to update the combo box with the new settings. I have a method that redraws the entire panel and reloads the combo box. But I don't know how to activate this method when the apply button is clicked in the settings class.

Here is a rough and tough example of what I am trying to accomplish.

Main class:

package testing;

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.Properties;

import javax.swing.*;

public class testConfigLoad extends JFrame
{
    JButton apply = new JButton("Apply");
JButton set   = new JButton("Settings");

    Properties          config      = new Properties();
    FileInputStream     fis         = null;
    FileOutputStream    fos         = null;
    final String        configFile  = "config.properties";

    OptPanel opt;

    public testConfigLoad() throws IOException
    {
        super("Test Program");
        setSize(200, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new FlowLayout());

        config();
        opt = new OptPanel(config);
        buildFrame();
    }

    public void buildFrame()
    {
        set.addActionListener(new setListener());

        add(opt);
        add(apply);
        add(set);

        setVisible(true);
    }

    public void config() throws IOException
    {
        try
        {
            fis = new FileInputStream(configFile);
            config.load(fis);
        }
        catch (FileNotFoundException e)
        {
            System.out.println("File not found");
        }
        finally
        {
            if (fis != null)
            {
                fis.close();
            }
        }       
    }

    private class setListener implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            settings set = new settings(config);
        }
    }

    public static void main(String[] args) throws IOException
    {
        new testConfigLoad();
    }
} 

      

Panel that needs updating:

package testing;

import java.util.Properties;
import javax.swing.*;

public class OptPanel extends JPanel
{
    String[] opts;
    JLabel optLabel = new JLabel("Available Options");
    Properties config;

    public OptPanel(Properties p)
    {
        config = p;
        opts = new String[3];
        buildPanel();
    }

    public void buildPanel()
    {
        for (int i = 0; i < opts.length; i++)
        {
            opts[i] = config.getProperty("option." + i + ".name");
        }

        JComboBox optBox = new JComboBox(opts);

        add(optLabel);
        add(optBox);
    }

    public void refPanel()
    {
        removeAll();
        this.buildPanel();
        ((JPanel) this).revalidate();
        repaint();
    }
}

      

And the settings class:

package testing;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Properties;
import javax.swing.*;

public class settings 
{
    Properties config;
    final String        configFile  = "config.properties";

    JFrame setFrame = new JFrame("Settings");
    JLabel opt1 = new JLabel("Option 1");
    JLabel opt2 = new JLabel("Option 2");
    JLabel opt3 = new JLabel("Option 3");
    JTextField text1 = new JTextField(15);
    JTextField text2 = new JTextField(15);
    JTextField text3 = new JTextField(15);
    JButton apply = new JButton("Apply");

    public settings(Properties p)
    {
        config = p;
        setFrame.setSize(275, 200);
        setFrame.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
        setFrame.setLayout(new FlowLayout());

        buildSetFrame();
    }

    public void buildSetFrame()
    {
        text1.setText(config.getProperty("option.0.name"));
        text2.setText(config.getProperty("option.1.name"));
        text3.setText(config.getProperty("option.2.name"));

        apply.addActionListener(new applyListener());

        setFrame.add(opt1);
        setFrame.add(text1);
        setFrame.add(opt2);
        setFrame.add(text2);
        setFrame.add(opt3);
        setFrame.add(text3);
        setFrame.add(apply);

        setFrame.setVisible(true);
    }

    private class applyListener implements ActionListener
    {
        public void actionPerformed(ActionEvent e) 
        {
            config.setProperty("option.0.name", text1.getText());
            config.setProperty("option.1.name", text2.getText());
            config.setProperty("option.2.name", text3.getText());

            FileOutputStream fos = null;
            try
            {
                fos = new FileOutputStream(configFile);
                config.store(fos, null);
            }
            catch (IOException f)
            {
                System.out.println("Error");
            }
            finally
            {
                if (fos != null)
                {
                    try
                    {
                        fos.close();
                    }
                    catch (IOException g)
                    {
                        System.out.println("Problem");
                    }
                }
            }
            setFrame.setVisible(false);

            //  This is where I need to pass something back to the 
                    //  testConfigLoad class to tell it to 
            //  run the refPanel method in the OptPanel class.
        }
    }
}   

      

The configuration file is called config.properties and looks like this:

option.2.name=two
option.1.name=one
option.0.name=zero

      

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1 answer


One approach is to use a callback between classes OptPanel

and settings

. You can extract functionality to add elements to properties JComboBox

in your own method:

public void updateProperties(Properties p) {
    model.removeAllElements();
    for (String s: p.stringPropertyNames()) {
        model.addElement(p.getProperty(s));
    }
}

      

where model

- DefaultComboBoxModel

. Then you can simply call

optPanel.updateProperties(config);

      



after successfully saving properties.


Some points:

  • The preferred approach is not to use multiple JFrames

    . One option is to use one JFrame

    with a modal dialog. See discussion .
  • Don't extend the JFrame, rather use the instance directly.
  • Java Naming conventions dictate that class names start with an uppercase letter, so settings

    will becomesettings

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