Thread: Let 'A' be an extension of JPanel, 'B' is a JPanel, and 'F' is a JFrame. Suppose B.add(A), and F.add(B). How do I access an ActionEvent, which occurs within 'A', from 'F'?

Hi there!

Here's the scenario:
+ Suppose we have a class GUI which extends JFrame and implements ActionListener.
+ We define a class Special_JPanel which extends JPanel.
+ A JComboBox, jCB, is a field in Special_JPanel.
+ A JPanel, baseJPnl, is a field in GUI.
+ A bunch of different components are placed into baseJPnl, including an instance of Special_JPanel.
+ The GUI class also functions as the driver class for my app.

The Problem:
+ A part of GUI's state needs to be dependent upon the ActionEvent which is generated by jCB ( e.g., If the user selects item 'a' from jCB, the GUI field 'm' is assigned value 'x', but if the user selects 'b' from jCB, 'm' is assigned value 'y'. )

The Current (Improper) Solution:
+ Set the access modifier of jCB to 'public' instead of 'private'. Then, it can be accessed directly from GUI.

The Query:
+ Aside form defining all of Special_JPanel within the body of GUI, is there a better way to solve this problem? I've been taught that the fields of a class must always be 'private' to maintain proper encapsulation.


Thanks in advance!
Chris

Here's code that uses the current (improper) solution:

import javax.swing.JPanel;
import javax.swing.JComboBox;
 
import java.awt.Dimension;
 
public class Special_JPanel extends JPanel{
 
	public JComboBox<String> jCB;
 
	public Special_JPanel(){
		setPreferredSize( new Dimension(200, 200) );
		String[] options = { "X", "Y" };
		jCB = new JComboBox<String>(options);
		jCB.setActionCommand("changeMode");
		add(jCB);
 
	}
 
	public static void main(String[] args) {}
}
 
//----------------------------------------------------------
import javax.swing.JFrame;
import javax.swing.JPanel;
 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.Dimension;
import java.awt.Color;
 
 
public class GUI extends JFrame implements ActionListener{
 
	private Special_JPanel sJP;
	private JPanel baseJPnl;
	private JPanel otherComponents;
 
	private Integer mode;
 
	public GUI(){
		otherComponents = new JPanel();
		otherComponents.setPreferredSize( new Dimension( 200, 300 ) );
 
		sJP = new Special_JPanel();
		baseJPnl = new JPanel();
		mode = 1;
 
		sJP.jCB.addActionListener(this);
	}
 
	public void createAndShowGUI(){
		update();
	}
 
	private void update(){
		revalidate();
 
		if (mode == 1){
			otherComponents.setBackground(Color.blue);
		}
		else{
			otherComponents.setBackground(Color.green);
		}
 
		baseJPnl.add(otherComponents);
		baseJPnl.add(sJP);
 
		add(baseJPnl);
 
		pack();
		setVisible(true);
	}
 
	public static void main(String[] args) {
		GUI g = new GUI();
		g.createAndShowGUI();
	}
 
	@Override
	public void actionPerformed(ActionEvent e) {
 
		if ( e.getActionCommand().equals("changeMode") ){
			if ( sJP.jCB.getSelectedItem().equals("X") ){
				mode = 1;
			}
			else if ( sJP.jCB.getSelectedItem().equals("Y") ){
				mode = 2;
			}
			update();
		}
	}
}

It's improper because the first class, Special_JPanel, has a field which is left as public. --And, this is done so that the first class can access the JComboBox, jCB, for the sake of 'hearing' its ActionEvent. While I have been taught that this is not the proper way to code in OOED languages, it's the only way that I have been able to make my driver class, GUI, respond to an event which occurs within Special_JPanel.

I'm sure that there's got to be some way to do this, but I've always found awt and javax.swing to be confusing.