import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class EjercicioPanel {

    JFrame winMain;
    JPanel jpMenBot;
    panel1 objPn1 = new panel1();
    panel2 objPn2 = new panel2();
    
    public EjercicioPanel(){
        
        winMain = new JFrame("EJERCICIO PANEL");
        winMain.setLayout(new BorderLayout(5, 5));
        
        menuBotones();       
        winMain.add(jpMenBot, BorderLayout.WEST);
        
        winMain.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        winMain.setPreferredSize(new Dimension(480, 500));
        winMain.setSize(480, 500);
        winMain.setLocation(200, 90);
        winMain.setVisible(true);
    }
    
    private void menuBotones(){
        
         jpMenBot = new JPanel(new GridLayout(2, 1, 10, 45));        
        
        JButton jbPan1 = new JButton("Panel 1");
        JButton jbPan2 = new JButton("Panel 2");
        
        jbPan1.setActionCommand("panel1"); jbPan2.setActionCommand("panel2");
        
        evenBoton eBtn = new evenBoton();
        
        jbPan1.addActionListener(eBtn); jbPan2.addActionListener(eBtn);
        
        jpMenBot.add(jbPan1); jpMenBot.add(jbPan2);        
        jpMenBot.setVisible(true);        
    }
    
    private class evenBoton implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {
            if(e.getActionCommand().equals("panel1") ){
                
                if(objPn2.pnPanel2 !=null && objPn2.pnPanel2.isVisible()){
                    
                    objPn2.pnPanel2.setVisible(false);
                    objPn1.mostrarPanel1();                
                    winMain.add(objPn1.pnPanel1, BorderLayout.CENTER);
                    objPn1.pnPanel1.setVisible(true);
                    winMain.pack();//ajusta la ventana y la visibilidad de sus componentes
                }else if(objPn2.pnPanel2 == null ){
                    
                    objPn1.mostrarPanel1();
                
                    winMain.add(objPn1.pnPanel1, BorderLayout.CENTER);
                    objPn1.pnPanel1.setVisible(true);
                    winMain.pack();//ajusta la ventana y la visibilidad de sus componentes
                }
            }else if(e.getActionCommand().equals("panel2")){
                
                if(objPn1.pnPanel1 != null && objPn1.pnPanel1.isVisible()){                    
                    
                    objPn1.pnPanel1.setVisible(false);
                    objPn2.mostrarPanel2();                
                    winMain.add(objPn2.pnPanel2, BorderLayout.CENTER);
                    objPn2.pnPanel2.setVisible(true);
                    winMain.pack();//ajusta la ventana y la visibilidad de sus componentes
                }else if(objPn1.pnPanel1==null){
                    objPn2.mostrarPanel2();
                
                    winMain.add(objPn2.pnPanel2, BorderLayout.CENTER);
                    objPn2.pnPanel2.setVisible(true);
                    winMain.pack();//ajusta la ventana y la visibilidad de sus componentes
                }
            }
        }
        
    }

    public static void main(String[] args) {
       
        EjercicioPanel objEjerPan = new EjercicioPanel();
    }
}

import java.awt.Panel;
import javax.swing.JLabel;


public class panel1 {
    
    Panel pnPanel1;
    
    public void mostrarPanel1(){
        
        pnPanel1 = new Panel();
        
        JLabel jlMostrarTxt1 = new JLabel("Hola gente de jagonzalez! n Este es el primer panel ;)");
        pnPanel1.add(jlMostrarTxt1);
        
        pnPanel1.setSize(150, 100);
        pnPanel1.setVisible(false);
    }
    
}

import java.awt.Panel;
import javax.swing.JLabel;

public class panel2 {
    
    Panel pnPanel2;
    
    public void mostrarPanel2(){
        
        pnPanel2 = new Panel();
        
        JLabel jlMostrarTxt1 = new JLabel("Hola gente de jagonzalez! n Este es el segundo panel ;)");
        pnPanel2.add(jlMostrarTxt1);
        
        pnPanel2.setSize(150, 100);
        pnPanel2.setVisible(false);
    }
    
}