Remove Java Panels without crashing your program

Question

So basically I am writing a GUI program that uses a JComboBox to display various finance formulas. I have everything in place in terms of it displaying the formulas but here is my problem. Everytime I go to choose a new formula in my comboBox it the other ones stay displayed. I've tried to write an if statement to disable, remove and invalidate these (not all at once) but none have worked...I need to get it so when I click a option the other panels disappear if there are any at all. Thanks!

Here is the full program the problem I am having is that when I choose a new formula the one that I chose before it is still active...I want to disable or remove it. Thanks.

import java.awt.BorderLayout;

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.text.DecimalFormat;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;





public class newFinanceFullClass extends JFrame {


           private JMenu fileMenu;
           private JMenuItem exitItem;

           private JPanel presentValuePanel;  
           private JPanel financeFinderPanel;// A panel container
           private JLabel principalMessage;  
           private JLabel yearlyRateMessage;
           private JLabel termYearMessage;
           private JPanel simpleInterestPanel;
           private JPanel doublingTimePanel;
           private JPanel compoundInterestPanel;
           private JLabel NONEMessage;
           private JLabel imageLabel;
           private JLabel label;// A message to display
           private JMenuBar menuBar;
           private JTextField principalText; // To hold user input
           private JButton calcButton;       // Performs calculation
           private final int WINDOW_WIDTH = 600;  // Window width
           private final int WINDOW_HEIGHT = 600; // Window height
           private JTextField yearlyRateText;
           private JTextField termYearText;
           DecimalFormat dc =new DecimalFormat("####0.00"); //formater 
           private JComboBox financeBox; 
           double principal = 400.0;
           double yearlyRate = .04;
           double termYears = 4.0;

           private String[] financeFormulas = { "NONE", "Present value", "Simple interest",
                   "Doubling time", "Compound interest", "Decaf"};


           financeFormulaClass financeFormula = new financeFormulaClass(principal, yearlyRate, termYears);

           /**
            *  Constructor
            */

           public newFinanceFullClass()
           {
              // Call the JFrame constructor.
              super("Finance Class");

              // Set the size of the window.
              setSize(WINDOW_WIDTH, WINDOW_HEIGHT);

              // Specify what happens when the close
              // button is clicked.
              setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

              // Build the panel and add it to the frame.
              financeFinderPanel();
              setLayout(new BorderLayout());

              //buildPanel();

              menuBar = new JMenuBar();
              buildFileMenu();
              menuBar.add(fileMenu);
              setJMenuBar(menuBar);

              // Add the panel to the frame's content pane.
              add(financeFinderPanel);
              //add(panel);

              // Display the window.
              setVisible(true);
           }

           private void financeFinderPanel()
           {
              // Create a panel to hold the combo box.


              financeFinderPanel = new JPanel();

              //create label
              label = new JLabel("Pick your formula");
              ImageIcon funnyImage = new ImageIcon("funny.gif");
              imageLabel = new JLabel();
              imageLabel.setLocation(50, 55);

              label.setForeground(Color.BLUE);
              // Create the combo box
              financeBox = new JComboBox(financeFormulas);
              imageLabel.setIcon(funnyImage);
              // Register an action listener.
              financeBox.addActionListener(new financeBoxListener());
              exitItem = new JMenuItem("Exit");   
              exitItem.setMnemonic(KeyEvent.VK_X);

              // Add the combo box to the panel.
              financeFinderPanel.add(financeBox);
              financeFinderPanel.add(label);
              financeFinderPanel.add(imageLabel);


           }

          /** private void menuList(){
            exitItem = new JMenuItem("Exit");   
            exitItem.setMnemonic(KeyEvent.VK_X);
            menuList.add(exitItem);
           } **/

           private void buildMenuBar()
           {
              // Create the menu bar.
              menuBar = new JMenuBar();

              // Create the file and text menus.
              buildFileMenu();
             // buildTextMenu();

              // Add the file and text menus to the menu bar.
              menuBar.add(fileMenu);
              //menuBar.add(textMenu);

              // Set the window's menu bar.
              setJMenuBar(menuBar);
           }





               private void buildFileMenu()
               {
                  // Create an Exit menu item.
                  exitItem = new JMenuItem("Exit");
                  exitItem.setMnemonic(KeyEvent.VK_X);
                  exitItem.addActionListener(new ExitListener());


                  // Create a JMenu object for the File menu.
                  fileMenu = new JMenu("File");
                  fileMenu.setMnemonic(KeyEvent.VK_F);

                  // Add the Exit menu item to the File menu.
                  fileMenu.add(exitItem);

               }





           private void presentValuePanel()
           {
              // Create the label, text field, and button components.
              principalMessage = new JLabel("principal");
              principalText = new JTextField(10);
              yearlyRateMessage = new JLabel("Yearly Rate");
              yearlyRateText = new JTextField(10);
              termYearMessage = new JLabel("Term Year");
              termYearText = new JTextField(10);
              calcButton = new JButton("Calc Present Value");

              // Add an action listener to the button.
              //calcButton.addActionListener(new CalcButtonListener());

              calcButton.addActionListener(new financeFormListener());

              // Create a panel to hold the components.
              presentValuePanel = new JPanel();

              // Add the label, text field, and button to the panel.
              presentValuePanel.add(principalMessage);
              presentValuePanel.add(principalText);
              presentValuePanel.add(yearlyRateMessage);
              presentValuePanel.add(yearlyRateText);
              presentValuePanel.add(termYearMessage);
              presentValuePanel.add(termYearText);
              presentValuePanel.add(calcButton);
           }


          private void simpleInterestPanel(){

               principalMessage = new JLabel("principal");
                  principalText = new JTextField(10);
                  yearlyRateMessage = new JLabel("Yearly Rate");
                  yearlyRateText = new JTextField(10);
                  termYearMessage = new JLabel("Term Year");
                  termYearText = new JTextField(10);
                  calcButton = new JButton("Calc Simple Interest");

                  simpleInterestPanel = new JPanel();
                  calcButton.addActionListener(new financeFormListener());

                  simpleInterestPanel.add(principalMessage);
                  simpleInterestPanel.add(principalText);
                  simpleInterestPanel.add(yearlyRateMessage);
                  simpleInterestPanel.add(yearlyRateText);
                  simpleInterestPanel.add(termYearMessage);
                  simpleInterestPanel.add(termYearText);
                  simpleInterestPanel.add(calcButton);



           }

          private void doublingTimePanel(){


              yearlyRateMessage = new JLabel("Yearly Rate");
              yearlyRateText = new JTextField(10);

              calcButton = new JButton("Calc Doubling Time");
              calcButton.addActionListener(new financeFormListener());


              doublingTimePanel = new JPanel();

              doublingTimePanel.add(yearlyRateMessage);
              doublingTimePanel.add(yearlyRateText);
              doublingTimePanel.add(calcButton);

          }

          private void compoundInterestPanel(){


              principalMessage = new JLabel("principal");
              principalText = new JTextField(10);
              yearlyRateMessage = new JLabel("Yearly Rate");
              yearlyRateText = new JTextField(10);
              termYearMessage = new JLabel("Term Year");
              termYearText = new JTextField(10);
              calcButton = new JButton("Calc Compound Interest");

              compoundInterestPanel = new JPanel();
              calcButton.addActionListener(new financeFormListener());

              compoundInterestPanel.add(principalMessage);
              compoundInterestPanel.add(principalText);
              compoundInterestPanel.add(yearlyRateMessage);
              compoundInterestPanel.add(yearlyRateText);
              compoundInterestPanel.add(termYearMessage);
              compoundInterestPanel.add(termYearText);
              compoundInterestPanel.add(calcButton);

          }


           //Listener to choose which formula

           private class financeBoxListener implements ActionListener
           {
              public void actionPerformed(ActionEvent e)
              {

                  Object actionCommand = e.getSource();
                  String selection = (String) financeBox.getSelectedItem();
                  if(selection.equals("Present value")){
                      //financeFinderPanel.removeAll();




                      presentValuePanel();
                      add(presentValuePanel, BorderLayout.SOUTH);

                      pack();


                  }



                 else if(selection.equals("Simple interest")){



                     simpleInterestPanel();
                     add(simpleInterestPanel, BorderLayout.NORTH);


                     pack();

                  }
                 else if(selection.equals("Doubling time")){
                     doublingTimePanel();
                     add(doublingTimePanel, BorderLayout.SOUTH);
                     pack();

                 }
                 else if(selection.equals("Compound interest")){

                    compoundInterestPanel();
                    add(compoundInterestPanel, BorderLayout.NORTH);
                    pack();

                 }
                 else if(selection.equals("NONE")){

                      setSize(200, 150);
                      financeFinderPanel();
                      add(financeFinderPanel, BorderLayout.NORTH);
                      NONEMessage = new JLabel("PICK A SELECTION");


                  }





              }
           }



           private class financeFormListener implements ActionListener{

            @Override
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub


                String actionCommand = e.getActionCommand();
                if(actionCommand.equals("Calc Simple Interest")){


                        try{
                        double principal = Double.parseDouble(principalText.getText());
                        double yearlyRate = Double.parseDouble(yearlyRateText.getText());
                        double termYears = Double.parseDouble(termYearText.getText());
                        double interestRate = (principal * yearlyRate * termYears);

                        String msg = "Simple interest is: $" + dc.format(interestRate);
                        JOptionPane.showMessageDialog(null, msg);
                        }
                        catch(NumberFormatException r){

                            JOptionPane.showMessageDialog(null, "Please insert formula information");

                        }

                }
                else if(actionCommand.equals("Calc Present Value"))


                {

                    try{
                double principal = Double.parseDouble(principalText.getText());
                double yearlyRate = Double.parseDouble(yearlyRateText.getText());
                double termYears = Double.parseDouble(termYearText.getText());

                double pValue = financeFormula.presentValue(principal, yearlyRate, termYears);
                //double pValue = principal * (((1- Math.pow(1 + yearlyRate, -termYears))/ yearlyRate));
                String msg = "Present value is: $" + dc.format(pValue);


                JOptionPane.showMessageDialog(null, msg);
                    }
                 catch(NumberFormatException r){

                     JOptionPane.showMessageDialog(null, "Please insert formula information");
                 }
                }

                else if(actionCommand.equals("Calc Doubling Time")){



                    try{
                    double yearlyRate = Double.parseDouble(yearlyRateText.getText());
                    double dValue = financeFormula.doublingTime(yearlyRate);
                    String msg = "Doubling Time is: " + dc.format(dValue);
                    JOptionPane.showMessageDialog(null, msg);
                    }
                    catch(NumberFormatException r){

                        JOptionPane.showMessageDialog(null, "Please insert formula information");
                    }
                }

                else if(actionCommand.equals("Calc Compound Interest")){

                    try{
                        double principal = Double.parseDouble(principalText.getText());
                        double yearlyRate = Double.parseDouble(yearlyRateText.getText());
                        double termYears = Double.parseDouble(termYearText.getText());
                        double compoundInterest = financeFormula.compoundInterest(principal, yearlyRate, termYears);
                        String msg = "Compound Interest is: $" + dc.format(compoundInterest);
                        JOptionPane.showMessageDialog(null, msg);
                    }
                    catch(NumberFormatException r){

                        JOptionPane.showMessageDialog(null, "Please insert formula information");

                    }
                }
                }






            }

           private class ExitListener implements ActionListener
            {
              public void actionPerformed(ActionEvent e)
              {
                 System.exit(0);
              }
            }














           public static void main(String[] args)
           {
              new newFinanceFullClass();
           }

}

Answer 1

Again, use a CardLayout to help you swap your JPanels. You would create a JPanel and set its layout to CardLayout, and then you'd add the JPanels (the "cards") that you wish to swap into this holder JPanel using String constants, Strings that you will pass into the CardLayout's show(...) method to allow it to swap your components.

For instance, say you had an enum to hold your financial formula Strings, something like:

public enum FinanceFormula {
    NONE("NONE"), 
    PRESENT_VALUE("Present value"), 
    SIMPLE_INTEREST("Simple interest"),
    DOUBLING_TIME("Doubling time"), 
    COMPOUND_INTEREST("Compound interest"), 
    DECAF("Decaf");

    private String name;

    private FinanceFormula(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return getName();
    };
}

Then the CardLayout and its JPanel could be set up like so:

private CardLayout cardLayout = new CardLayout();
private JPanel cardHolderPanel = new JPanel(cardLayout);

and the JComboBox like below. This works because I have overridden the enum's to String method so that a proper name will display:

private JComboBox<FinanceFormula> comboBox = new JComboBox<>(FinanceFormula.values());

You would then add all the formula JPanels into the cardHolderPanel using String constants obtained from the enum:

// fill the cardHolderPanel with "cards", JPanels with formula:
cardHolderPanel.add(createNonePanel(), FinanceFormula.NONE.getName());
cardHolderPanel.add(createPresentValuePanel(), FinanceFormula.PRESENT_VALUE.getName());
cardHolderPanel.add(createSimpleInterestPanel(), FinanceFormula.SIMPLE_INTEREST.getName());
cardHolderPanel.add(createDoublingTimePanel(), FinanceFormula.DOUBLING_TIME.getName());
cardHolderPanel.add(createCompoundInterestPanel(), FinanceFormula.COMPOUND_INTEREST.getName());
cardHolderPanel.add(createDecafPanel(), FinanceFormula.DECAF.getName());

Then when you want to swap JPanels, simply pass in the appropriate String into the CardLayout's show method, and you're good:

private void combBoxActionPerformed(ActionEvent e) {
    FinanceFormula selectedFormula = (FinanceFormula) comboBox.getSelectedItem();
    cardLayout.show(cardHolderPanel, selectedFormula.getName());
}

The following program doesn't create any fancy formula JPanels, but it doesn't have to, since it is an MCVE built to demonstrate swapping JPanels only:

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class NewFinance2 extends JPanel {
    private CardLayout cardLayout = new CardLayout();
    private JPanel cardHolderPanel = new JPanel(cardLayout);
    private JComboBox<FinanceFormula> comboBox = new JComboBox<>(FinanceFormula.values());

    public NewFinance2() {
        // fill the cardHolderPanel with "cards", JPanels with formula:
        cardHolderPanel.add(createNonePanel(), FinanceFormula.NONE.getName());
        cardHolderPanel.add(createPresentValuePanel(), FinanceFormula.PRESENT_VALUE.getName());
        cardHolderPanel.add(createSimpleInterestPanel(), FinanceFormula.SIMPLE_INTEREST.getName());
        cardHolderPanel.add(createDoublingTimePanel(), FinanceFormula.DOUBLING_TIME.getName());
        cardHolderPanel.add(createCompoundInterestPanel(), FinanceFormula.COMPOUND_INTEREST.getName());
        cardHolderPanel.add(createDecafPanel(), FinanceFormula.DECAF.getName());

        comboBox.addActionListener(e -> combBoxActionPerformed(e));
        JPanel northPanel = new JPanel();
        northPanel.add(comboBox);

        setLayout(new BorderLayout());
        add(cardHolderPanel, BorderLayout.CENTER);
        add(northPanel, BorderLayout.NORTH);
    }

    private void combBoxActionPerformed(ActionEvent e) {
        FinanceFormula selectedFormula = (FinanceFormula) comboBox.getSelectedItem();
        cardLayout.show(cardHolderPanel, selectedFormula.getName());
    }


    // A bunch of dummy methods that don't create much
    // Your real methods would create more complex JPanels
    private JPanel createDecafPanel() {
        return createPanel(FinanceFormula.DECAF);
    }

    private JPanel createCompoundInterestPanel() {
        return createPanel(FinanceFormula.COMPOUND_INTEREST);
    }

    private JPanel createDoublingTimePanel() {
        return createPanel(FinanceFormula.DOUBLING_TIME);
    }

    private JPanel createSimpleInterestPanel() {
        return createPanel(FinanceFormula.SIMPLE_INTEREST);
    }

    private JPanel createPresentValuePanel() {
        return createPanel(FinanceFormula.PRESENT_VALUE);
    }

    private JPanel createNonePanel() {
        return createPanel(FinanceFormula.NONE);
    }   

    // temporary method just for demonstration purposes
    private JPanel createPanel(FinanceFormula financeFormula) {
        JLabel label = new JLabel(financeFormula.getName());
        label.setFont(label.getFont().deriveFont(Font.BOLD, 24f));

        JPanel panel = new JPanel(new GridBagLayout());
        panel.add(label);
        panel.setPreferredSize(new Dimension(400, 300));
        float split = 0.7f;
        float h = (float) (split + Math.random() * (1f - split));
        float s = (float) (split + Math.random() * (1f - split));
        float b = (float) (split + Math.random() * (1f - split));
        Color color = Color.getHSBColor(h, s, b);
        panel.setBackground(color);
        return panel;
    }

    private static void createAndShowGui() {
        NewFinance2 mainPanel = new NewFinance2();

        JFrame frame = new JFrame("Finance");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}