Accessing JFrame from seperat file?

[soulmed]

I've built a simple programe to illustrat my problem. I'm trying to use a JFrame in my mane page and to build my JPanel in a seperat file. My problem is that I can't find how to switch JPanel from the seperate file.

Here's my 3 pages:

test.java

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

public class test {
	public static JFrame frame = new JFrame ("MyPanel");
    
	public static void main (String[] args) {
        page1 MyPanel1 = new page1();
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add (MyPanel1);
        frame.pack();
        frame.setVisible (true);
    }
}

page1.java

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class page1 extends JPanel {
	
	public page1() {

    	JButton page1BTN = new JButton ("Page 1");
        page1BTN.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
            	page1BTN_Clicked(e);
            }
        });
        
        setPreferredSize (new Dimension (234, 175));
        setLayout (null);
        add (page1BTN);

        page1BTN.setBounds (55, 70, 100, 20);
    }

    protected void page1BTN_Clicked(ActionEvent e) {
    	page2 MyPanel2 = new page2();
		super.removeAll();
    	super.add(MyPanel2);
    	super.validate();
	}

}

page2.java

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class page2 extends JPanel{
	
	public page2()  {

        JButton page2BTN = new JButton ("Page 2");
        page2BTN.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
            	page2BTN_Clicked(e);
            }
        });
        
        setPreferredSize (new Dimension (234, 175));
        setLayout (null);
        add (page2BTN);

        page2BTN.setBounds (55, 70, 100, 20);
    }
	
    protected void page2BTN_Clicked(ActionEvent e) {
    	page1 MyPanel1 = new page1();
    	super.removeAll();
    	super.add(MyPanel1);
    	super.validate();
	}
}

[Fubarable]

Please see similar active threads that address this. For instance: JFrame and CardLayout -- Wrong Parent

[soulmed]

For those out there with the same problem reading this thread, here's my working code:

test.java

import javax.swing.*;

public class test {
	public static JFrame frame = new JFrame ("MyPanel");
	public static void main (String[] args) {
        page1 MyPanel1 = new page1();
        
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add (MyPanel1.getPanel());
        frame.pack();
        frame.setVisible (true);
    }
	public static void changePanel(JPanel jp){
		//JOptionPane.showMessageDialog(null,frame);
		frame.getContentPane().removeAll();		
        frame.getContentPane().add (jp);
        frame.pack();
        frame.validate();
	}
}

page1.java

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

public class page1 extends test {
	
	public page1() {
	}
	public JPanel getPanel(){
		JPanel jp = new JPanel();
    	JButton page1BTN = new JButton ("Page 1");
        page1BTN.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
            	page2 MyPanel2 = new page2();
            	changePanel(MyPanel2.getPanel());
            }
        });
        
        jp.setPreferredSize (new Dimension (234, 175));
        jp.setLayout (null);
        jp.add (page1BTN);

        page1BTN.setBounds (55, 70, 100, 20);
        return jp;
    }

}

page2.java

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

public class page2 extends test{
	
	public page2()  {
	}
	public JPanel getPanel(){
		JPanel jp = new JPanel();
        JButton page2BTN = new JButton ("Page 2");
        page2BTN.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
            	page1 MyPanel1 = new page1();
            	changePanel(MyPanel1.getPanel());
            }
        });
        
        jp.setPreferredSize (new Dimension (200, 150));
        jp.setLayout (null);
        jp.add (page2BTN);

        page2BTN.setBounds (55, 70, 100, 20);
        return jp;
    }
	
}

[Fubarable]

The problem I have with your code is that you repeatedly recreate your two JPanels for no reason. Why not simply use a CardLayout and swap JPanels based on a constant String. e.g.,

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class Test2 {
   private static void createAndShowUI() {
      JFrame frame = new JFrame("Test2");
      frame.getContentPane().add(new MainPanel());
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {
         public void run() {
            createAndShowUI();
         }
      });
   }
}

class MainPanel extends JPanel {
   public static final String SUB_PANEL_1 = "Sub Panel 1";
   public static final String SUB_PANEL_2 = "Sub Panel 2";
   private SubPanel subPanel1 = new SubPanel(this, SUB_PANEL_1, SUB_PANEL_2);
   private SubPanel subPanel2 = new SubPanel(this, SUB_PANEL_2, SUB_PANEL_1);
   private CardLayout cardlayout = new CardLayout();
   
   public MainPanel() {
      setLayout(cardlayout);
      add(subPanel1, SUB_PANEL_1);
      add(subPanel2, SUB_PANEL_2);
   }
   
   public void swapPanel(String nextPanelName) {
      cardlayout.show(this, nextPanelName);
   }
}

class SubPanel extends JPanel {
   private MainPanel mainPanel;
   private String nextPanelName;

   public SubPanel(MainPanel mainPanel, String thisPanelName, String nextPanelName) {
      this.mainPanel = mainPanel;
      this.nextPanelName = nextPanelName;      
      
      JButton nextPanelBtn = new JButton("Show " + nextPanelName);
      nextPanelBtn.addActionListener(new ActionListener() {
         @Override
         public void actionPerformed(ActionEvent e) {
            nextPanelBtnActionPerformed();
         }
      });
      JPanel holdingPanel = new JPanel(new GridBagLayout());
      holdingPanel.setPreferredSize(new Dimension(200, 150));
      holdingPanel.add(nextPanelBtn);
      
      setLayout(new BorderLayout());
      add(new JLabel(thisPanelName, SwingConstants.CENTER), BorderLayout.NORTH);
      add(holdingPanel, BorderLayout.CENTER);
   }

   private void nextPanelBtnActionPerformed() {
      mainPanel.swapPanel(nextPanelName);
   }
   
}

[soulmed]

I might be wrong. I'm still new to Java.

The reason why I did it this way is that if my program has lots of pages, that would represent lots of memory space occupied by unused pages.

Am I right?

[Fubarable]

Your way creates more objects and wastes more space.

[RichersooN]

#1. You can create panel from class1 then create a method in class2 that has a parameter of jpanel then add that to the class2's jframe