Issues with GUI on a permutation/combination calculator

Question

I was able to program this, and I don't have any errors that I can see, and it even displays the gui. I'm pretty sure I assigned the buttons properly. But the GUI is temperamental, and when I run it, it displays but sometimes the insides of the gui disappear when I enter values. But it calculates nCr, just not pCr.

I have a driver class. Pretty sure it's implemented properly. Here's my panel class. I'm wondering what's wrong and why the GUI doesn't function properly

I realize this is a lot of code. I'm not expecting anyone to rewrite this for me. I just want to know what I'm doing wrong, and how I can go about correcting it.

Thanks.

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





public class PermCombCalc extends JPanel {
    JButton permButton = new JButton();
    JButton combButton = new JButton();
    JButton clearButton = new JButton();

    JTextField npermField = new JTextField();
    JTextField rperField = new JTextField();
    JTextField nchooseField = new JTextField();
    JTextField rchooseField = new JTextField();

    JTextField pAnswerField = new JTextField();
    JTextField cAnswerField = new JTextField();




    public PermCombCalc() {

        setLayout(new BorderLayout());
        setPreferredSize(new Dimension(1000, 700));

        JLabel permLabel = new JLabel("Permutation:");
        permLabel.setBounds(10, 20, 100, 20);
        permLabel.setForeground(Color.BLACK);
        add(permLabel);

        JLabel combLabel = new JLabel("Combination:");
        combLabel.setBounds(215, 20, 75, 20);
        combLabel.setForeground(Color.BLACK);
        add(combLabel);

        // Creating Permutation Button
        JLabel PnrLabel = new JLabel("P (n,r)");
        PnrLabel.setForeground(Color.black);
        permButton.setBounds(10, 115, 100, 25);
        add(permButton);
        permButton.add(PnrLabel);
        // Action Listener for permbutton
        permButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                permButton.setActionCommand("Perm");
                permButton.addActionListener(new ButtonListener());

            }

        });

        // Creating combination button
        JLabel CnrLabel = new JLabel("C(n, r)");
        CnrLabel.setForeground(Color.black);
        combButton.setBounds(190, 115, 100, 25);
        add(combButton);
        combButton.add(CnrLabel);
        // ActionListener
        combButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                combButton.setActionCommand("comb");
                combButton.addActionListener(new ButtonListener());


            }
        });

        // Text fields for n and r

        npermField.setBounds(23, 50, 60, 20);
        add(npermField);
        nchooseField.setBounds(230, 50, 60, 20);
        add(nchooseField);

        rperField.setBounds(23, 80, 60, 20);
        add(rperField);
        rchooseField.setBounds(230, 80, 60, 20);
        add(rchooseField);

        // Input fields

        JLabel npLabel = new JLabel("n:");
        npLabel.setForeground(Color.black);
        npLabel.setBounds(10, 55, 10, 10);
        add(npLabel);

        JLabel ncLabel = new JLabel("n:");
        ncLabel.setForeground(Color.BLACK);
        ncLabel.setBounds(217, 55, 10, 10);
        add(ncLabel);

        JLabel rpLabel = new JLabel("r:");
        rpLabel.setForeground(Color.BLACK);
        rpLabel.setBounds(10, 85, 10, 10);
        add(rpLabel);

        JLabel rcLabel = new JLabel("r:");
        rcLabel.setForeground(Color.BLACK);
        rcLabel.setBounds(217, 85, 10, 10);
        add(rcLabel);

        // Fields for answers

        JLabel pAnswerJLabel = new JLabel("<-Answers->");
        pAnswerJLabel.setForeground(Color.BLACK);
        pAnswerJLabel.setBounds(115, 155, 74, 10);
        add(pAnswerJLabel);
        pAnswerField.setBounds(10, 150, 100, 20);
        add(pAnswerField);


        cAnswerField.setBounds(190, 150, 100, 20);  // where is this field?!
        add(cAnswerField);

        // Buttons

        //clearButton.setBounds(10, 210, 110, 25);
        //add(clearButton);

        //JLabel clearLabel = new JLabel("Clear Fields");
        //clearLabel.setForeground(Color.BLACK);
        //clearButton.add(clearLabel);
        // clearButton.addActionListener(new ActionListener() {
        // public void actionPerformed(ActionEvent e) {
        // clearButton.setActionCommand("Clear");

    }
private class ButtonListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        if (e.getActionCommand().equals("perm")) {
            // contentPane.setBackground(Color.red);
            long Pnr = Permutation();
            if (Pnr != 0) {
                pAnswerField.setText(Pnr + "");
            }
        } else if (e.getActionCommand().equals("comb")) {
            // contentPane.setBackground(Color.black);
            long Cnr = Combination();
            if (Cnr != 0) {
                cAnswerField.setText(Cnr + "");

            }
        } else if (e.getActionCommand().equals("Clear")) {
            // contentPane.setBackground(Color.lightGray);
            npermField.setText(null);
            rperField.setText(null);
            pAnswerField.setText(null);
            nchooseField.setText(null);
            rchooseField.setText(null);
            cAnswerField.setText(null);
        }

    }

    public long Permutation() {
        String npString = npermField.getText();
        String rpString = rperField.getText();
        int npint = 0;
        int rpint = 0;

        try {
            npint = Integer.parseInt(npString);
            rpint = Integer.parseInt(rpString);
        } catch (NumberFormatException e) {
            JOptionPane.showMessageDialog(null,"ERROR! The values for 'n' and 'r' \n must be positive integers");
            return 0;
        }
        if (npint <= 0 || rpint <= 0) {
            JOptionPane.showMessageDialog(null,"ERROR! The values for 'n' and 'r' \n must be positive integers");
            return 0;
        }
        if (npint < rpint) {
            JOptionPane.showMessageDialog(null,"ERROR! The value of 'r' must be less than \n or equal to the value of 'n.'");
            return 0;
        }

        long Pnr = 1;
        int mult = npint;
        int nmr = (npint - rpint);
        while (mult > nmr) {
            Pnr = Pnr * mult;
            mult--;
        }

        return Pnr;
    }

    public long Combination()  {
        String ncString = nchooseField.getText();
        String rcString = rchooseField.getText();
        int ncint = 0;
        int rcint = 0;

        try {
            ncint = Integer.parseInt(ncString);
            rcint = Integer.parseInt(rcString);
        } catch (NumberFormatException e) {
            JOptionPane.showMessageDialog(null,"ERROR! The values for 'n' and 'r' \n must be positive integers");
            return 0;
        }
        if (ncint <= 0 || rcint <= 0) {
            JOptionPane.showMessageDialog(null,"Error! The values for 'n' and 'r' \n must be positive integers");
            return 0;
        }
        if (ncint < rcint) {
            JOptionPane.showMessageDialog(null,"ERROR! The value of 'r' must be less than \n or equal to the value of 'n.'");
            return 0;
        }

        long nfact = 1;
        for (int i = 2; i <= ncint; i++) {
            nfact = nfact * i;
        }
        long rfact = 1;
        for (int i = 2; i <= rcint; i++) {
            rfact = rfact * i;
        }
        long nmr = ncint - rcint;
        int nmrfact = 1;
        for (int i = 2; i <= nmr; i++) {
            nmrfact = nmrfact * i;
        }

        long Cnr = (nfact / (rfact * nmrfact));

        return Cnr;

    }

}
}

Answer 1

You are using BorderLayout, but you aren't actually specifying the placements of your components, so they are being rendered in unexpected places.

Here is a screenshot of your application with an orange border around pAnswerField and a red border around cAnswerField

You should take a look at the A Visual Guide to Layout Managers for help on using the Layout Managers properly.

For your application, GridLayout is probably a resonable balance between complexity and layout flexibility

GridBagLayout or SpringLayout will give you the most flexibility, but they can be frustratingly complex to work with.

EDIT Another minor problem which is causing the permButton to misbehave.

In your button creation code you have: permButton.setActionCommand("Perm");

In your action listener you have: if (e.getActionCommand().equals("perm"))

As written your ActionListener will never get invoked when permButton gets pressed... Either switch to equalsIgnoreCase or define a constant rather than using string literals.

I find adding colored borders to be very helpful when doing layout work. Here's a quick example of how to do this:

npermField.setBounds(23, 50, 60, 20);
add(npermField);
nchooseField.setBounds(230, 50, 60, 20);

// add a border to make the component easier to see during layout.
npermField.setBorder(BorderFactory.createLineBorder(Color.ORANGE));

add(nchooseField);