Thread: Calculate Button Not Working

Hello, I am new to java and for a school project due Monday, I have to create a program that calculates the mortgage and displays each months payments in a table below the reset and calculate buttons. My problem is that I cannot get the calculate button to work and I have no idea what is wrong as eclipse only brings up an error when the calculate button is pressed. Here is my code, thanks for helping me with this. By the way, I apologize about it being messy.

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;
 
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.table.DefaultTableModel;
 
public class JamesProctorProgramGUIWk3 extends JFrame implements ActionListener{
 
 
/**
	 * 
	 */
private static final long serialVersionUID = 1L;
 
//Loan Values
double principalPaid; 
double currentInter;
double balanceAmount;
double monthPrincipal; 
double interestRate;	
double paymentField;  
double monthInterest; 
double[] interRate = {0.0535, 0.0550, 0.0575}; 
int[] yearRate = {7, 15, 30}; 
int termYears, termMonths, i = 0, m = 0, done;
int monthAmount; 
String[] rate = {"7 year at 5.35%", "15 year at 5.5%", "30 year at 5.75%"};
String principalAmount;
 
//text fields
JTextField loanField = new JTextField("", 7);  
JTextField monthField = new JTextField("", 7); 
 
 
 
//creates the panel
JPanel contentPanel;
 
//creates the reset and calculate buttons
JButton calculateButton, resetButton;
 
//creates labels
JLabel loanAmountlbl, monthlyPaymentlbl;
 
//Sets Decimal Format
DecimalFormat paymentFormat = new DecimalFormat ("$###,##0.00");;
 
//create combo box
JComboBox percentBox = new JComboBox();
 
//creates table format
DefaultTableModel model = new DefaultTableModel();
JTable table = new JTable(model);
 
//creates GUI
public JamesProctorProgramGUIWk3()
{
	super();
	createGUI();
}
	public void createGUI()
	{
		this.setSize(700, 300); //length, height
		this.setLocation(0, 0); //this specifies where the frame position will be on the screen
		this.setContentPane(contentPanel());
		this.setTitle("James Proctor Program GUI Wk3");
	}
    public JPanel contentPanel()
    {
    	contentPanel = new JPanel();
        contentPanel.setLayout(null);
 
        //adds labels to the panel
        loanAmountlbl = new JLabel("Mortgage:");
        loanAmountlbl.setLocation(200, 30);
        loanAmountlbl.setSize(100, 25);
        contentPanel.add(loanAmountlbl);
 
        monthlyPaymentlbl = new JLabel("Monthly Payment:");
        monthlyPaymentlbl.setLocation(158, 85);
        monthlyPaymentlbl.setSize(100, 30);
        contentPanel.add(monthlyPaymentlbl);
 
 
        //adds text fields
        loanField = new JTextField("", 10);
        loanField.setLocation(280, 30);
        loanField.setSize(150, 25);
        contentPanel.add(loanField);
 
        monthField = new JTextField("", 10);
        monthField.setLocation(280, 85);
        monthField.setSize(150, 25);
        contentPanel.add(monthField);
 
        //this adds the combo box and action listener
        percentBox.addItem(rate[0]);
        percentBox.addItem(rate[1]);
        percentBox.addItem(rate[2]);
        percentBox.setLocation(280, 55);
        percentBox.setSize(150, 25);
        percentBox.addActionListener(this);
        contentPanel.add(percentBox);
 
        //adds a scrollbar
        JScrollPane scroller = new JScrollPane(table);
        contentPanel.add(scroller);
        scroller.setSize(650,300);
        scroller.setLocation(20, 150);
 
        //adds column names to the table
        model.addColumn("Payment Number");
        model.addColumn("Current Interest");
        model.addColumn("Principal Paid");
        model.addColumn("New Balance");
 
 
        //setup up buttons
        resetButton = new JButton("Reset");
        resetButton.setLocation(450, 55);
        resetButton.setSize(100, 25);
        contentPanel.add(resetButton);
 
 
        calculateButton = new JButton("Calculate");
        calculateButton.setLocation(450, 85);
        calculateButton.setSize(100, 25);
        contentPanel.add(calculateButton);
 
 
        calculateButton.addActionListener(this);
        resetButton.addActionListener(this);
        return contentPanel;
    }
 
    //action event for the calculate button
    public void actionPerformed(ActionEvent e)
    {
 
            String calculate = e.getActionCommand();
            if (e.getSource() == percentBox) {
            	switch (percentBox.getSelectedIndex()){
            case 0:
                    i = 0;
                    break;
            case 1:
                    i = 1;
                    break;
            case 2:
                    i = 2;
                    break;
            }
        }
            if (calculate == "Calculate")
            {
            	loanField.setText("");
            	principalAmount = monthField.getText();
 
            	//cannot get the calculate button to function 
            	//error has to do with the below line of code
            		monthPrincipal = Double.parseDouble(principalAmount);
            }
            if(done == 1)
                    done = 0;
            else {
                            interestRate = interRate[i];
 
                            termYears = yearRate[i];
 
                            monthInterest = interestRate/(12*100); //finds the monthly interest
 
                            termMonths = termYears*12; //calculates term length in months
 
                            paymentField = monthInterest*monthPrincipal/(1-Math.pow((1+monthInterest), -termMonths)); //calculates monthly payment
 
                            loanField.setText(" " + paymentFormat.format(paymentField));
 
                            //loop for the table to display each payment
                            for (m = 0; m <= monthAmount; m ++) {
 
                            	monthAmount = yearRate[i]*12;
 
                            	currentInter = monthPrincipal * monthInterest;
 
                            	principalPaid = paymentField - currentInter;
 
                            	balanceAmount = monthPrincipal - principalPaid;
 
                            	monthPrincipal = balanceAmount;
 
                                if(monthPrincipal <= 1){ break;}
 
                            	model.addRow(new Object[]{m+1, paymentFormat.format(currentInter), paymentFormat.format(principalPaid), paymentFormat.format(balanceAmount)});
 
                                if(monthPrincipal <= 1){ break;}
 
            }
            }
            //action event for the reset button
            //this button does work
            if (e.getSource() == resetButton)
            {
                loanField.setText(""); 
                monthField.setText(""); 
                loanField.requestFocusInWindow(); 
                percentBox.setSelectedIndex(0);
 
                model.setRowCount(0);
            }
    }
 
            //shows the GUI
public static void main(String[] args){
	new JamesProctorProgramGUIWk3().setVisible(true);
	}
}

Copy and paste the error message here.

... and tell us which line in your source the line numbers in the error message refer to.

for a school project due Monday

You're asking a question whole days before your assignment is due? I think you must be the best student to ever post a question here

Here is the error:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String

I fixed this error with a try and catch, but now the button does not calculate anything. It just places 0.00 as the answer, and it does not display anything in the table.
Do you need the entire source again or just the section pertaining to the try and catch and the calculations?

That looks like only part of the message. The rest of the message has the source code line number where the error occured.

Did the error occur on statement that was trying to convert a String to a number and the String was empty? You need to add code to test if the String is empty BEFORE trying to convert it to a number.
If the String is empty, don't try to convert it. Hint: use an if test

Otherwise post the code where the error occurred.

I have it now where the Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String, error no longer pops up. However, no matter the number I place in the loanField text field, the code I use for the exception happens. I am thinking that the reason has to do with the code from line 164 to 197, as that is the exception handler and calculation part of the code.

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;
 
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.table.DefaultTableModel;
 
public class JamesProctorGUIWk3 extends JFrame implements ActionListener{
 
 
/**
	 * 
	 */
private static final long serialVersionUID = 1L;
 
//Loan Values
double principalPaid; 
double currentInter;
double balanceAmount;
double monthPrincipal; 
double interestRate;	
double paymentField;  
double monthInterest; 
double[] interRate = {0.0535, 0.0550, 0.0575}; 
int[] yearRate = {7, 15, 30}; 
int termYears, termMonths, i = 0, m = 0, done;
int monthAmount; 
String[] rate = {"7 year at 5.35%", "15 year at 5.5%", "30 year at 5.75%"};
String principalAmount;
 
//text fields
JTextField loanField = new JTextField("", 7);  
JTextField monthField = new JTextField("", 7); 
 
//java.lang.NumberFormatException
 
//creates the panel
JPanel contentPanel;
 
//creates the reset and calculate buttons
JButton calculateButton, resetButton;
 
//creates labels
JLabel loanAmountlbl, monthlyPaymentlbl;
 
//Sets Decimal Format
DecimalFormat paymentFormat = new DecimalFormat ("$###,##0.00");;
 
//create combo box
JComboBox percentBox = new JComboBox();
 
//creates table format
DefaultTableModel model = new DefaultTableModel();
JTable table = new JTable(model);
 
//creates GUI
public JamesProctorGUIWk3()
{
	super();
	createGUI();
}
	public void createGUI()
	{
		this.setSize(700, 300); //length, height
		this.setLocation(0, 0); //this specifies where the frame position will be on the screen
		this.setContentPane(contentPanel());
		this.setTitle("James Proctor Program GUI Wk3");
	}
    public JPanel contentPanel()
    {
    	contentPanel = new JPanel();
        contentPanel.setLayout(null);
 
        //adds labels to the panel
        loanAmountlbl = new JLabel("Mortgage:");
        loanAmountlbl.setLocation(200, 30);
        loanAmountlbl.setSize(100, 25);
        contentPanel.add(loanAmountlbl);
 
        monthlyPaymentlbl = new JLabel("Monthly Payment:");
        monthlyPaymentlbl.setLocation(158, 85);
        monthlyPaymentlbl.setSize(100, 30);
 
        contentPanel.add(monthlyPaymentlbl);
 
 
        //adds text fields
        loanField = new JTextField("", 10);
        loanField.setLocation(280, 30);
        loanField.setSize(150, 25);
        contentPanel.add(loanField);
 
        monthField = new JTextField("", 10);
        monthField.setLocation(280, 85);
        monthField.setSize(150, 25);
       // monthField.setEditable(false);
        contentPanel.add(monthField);
 
        //this adds the combo box and action listener
        percentBox.addItem(rate[0]);
        percentBox.addItem(rate[1]);
        percentBox.addItem(rate[2]);
        percentBox.setLocation(280, 55);
        percentBox.setSize(150, 25);
        percentBox.addActionListener(this);
        contentPanel.add(percentBox);
 
        //adds a scrollbar
        JScrollPane scroller = new JScrollPane(table);
        contentPanel.add(scroller);
        scroller.setSize(650,300);
        scroller.setLocation(20, 150);
 
        //adds column names to the table
        model.addColumn("Payment");
        model.addColumn("Interest");
        model.addColumn("Principal");
        model.addColumn("Balance");
 
 
        //setup up buttons
        resetButton = new JButton("Reset");
        resetButton.setLocation(450, 55);
        resetButton.setSize(100, 25);
        contentPanel.add(resetButton);
 
 
        calculateButton = new JButton("Calculate");
        calculateButton.setLocation(450, 85);
        calculateButton.setSize(100, 25);
        contentPanel.add(calculateButton);
 
 
        calculateButton.addActionListener(this);
        resetButton.addActionListener(this);
        return contentPanel;
    }
 
    //action event for the calculate button
    public void actionPerformed(ActionEvent e)
    {
 
            String calculate = e.getActionCommand();
            if (e.getSource() == percentBox) {
            	switch (percentBox.getSelectedIndex()){
            case 0:
                    i = 0;
                    break;
            case 1:
                    i = 1;
                    break;
            case 2:
                    i = 2;
                    break;
            }
        }
            if (calculate == "Calculate")
            {
            	loanField.setText("");
            	principalAmount = monthField.getText();
 
            	try
            	{
            		monthPrincipal = Double.parseDouble(principalAmount);
            		if (monthPrincipal <= 0) throw new NumberFormatException();
            	}
 
            	catch (NumberFormatException a){
            		monthField.setText("Number must be greater than 0");
            	}}{
 
 
                            //loop for the table to display each payment
                            for (m = 0; m <= monthAmount; m ++) {
 
                            	monthAmount = yearRate[i]*12;
 
                            	currentInter = monthPrincipal * monthInterest;
 
                            	principalPaid = paymentField - currentInter;
 
                            	balanceAmount = monthPrincipal - principalPaid;
 
                            	monthPrincipal = balanceAmount;
 
                                if(monthPrincipal <= 1){ break;}
 
                            	model.addRow(new Object[]{m+1, paymentFormat.format(currentInter), paymentFormat.format(principalPaid), paymentFormat.format(balanceAmount)});
 
                                if(monthPrincipal <= 1){ break;}
 
            }
 
            //action event for the reset button
            //this button does work
            if (e.getSource() == resetButton)
            {
                loanField.setText(""); 
                monthField.setText(""); 
                loanField.requestFocusInWindow(); 
                percentBox.setSelectedIndex(0);
 
                model.setRowCount(0);
            }}}
 
 
 
			//shows the GUI
public static void main(String[] args){
	new JamesProctorGUIWk3().setVisible(true);
	}
}

If you get errors please copy and paste the full text of the message here.

You should check if principalAmount is empty BEFORE trying to convert it.

Your throwing and catching the NumberFormatException in the next statement is silly. Why not just print out the message when you detect the error?

I finally figured it out. I had the loanField and monthField variables mixed up. For the heck of it, I decided to enter a number into the monthly payment text field instead of the mortgage field and it worked as intended with no errors.

This thread is solved, but there is no option in the thread menu for me to mark it as such. Is there another way?