The member variables are float[] which are sent to the GraphPanel. The calculations in the amortizeButton ActionListener block are done in double precision. The member variables arrays can be (cast to float and) loaded in the amorization for loop.
You had a member variable declaration which I removed. It was used in the graphButton AcitionListener block. I put in a JDialog instead and declared it as a local variable. You can put it back if you like.
Also, unrelated, the non–editable monthlyPayment textField looks a little dim. You could set it nonFocusable instead. Or use a JLabel.
import java.awt.*;
import java.awt.event.*;
import java.awt.font.*;
import java.awt.geom.*;
import java.io.*;
import java.text.*;
import javax.swing.*;
import javax.swing.border.*;
public class MC extends JFrame implements ActionListener {
JTextField principalTxt, termTxt, rateTxt, monthlyPaymentTxt;
JTextArea displayArea;
JButton calculateButton, graphButton, amortizeButton, clearButton, exitButton;
JComboBox options;
//formatting variables
DecimalFormat df = new DecimalFormat("\u00A4#,##0.00"); //currency
DecimalFormat pf = new DecimalFormat("#,##0.00%"); //percentages
DecimalFormat mi = new DecimalFormat("#,##0.000%"); //percentages
// Can these 6 be removed and declared as local variables?
int term = 0;
double principal = 0;
double rate = 0;
double monthlyPayment = 0;
double interest = 0;
int notePeriod = 0;
int[] termArray;
double[] rateArray;
private float[] principalAmts;
private float[] interestAmts;
public MC() {
super ("Mortgage Payment Calculator by S Kemen");
load();
// Initialize components.
JPanel row1 = new JPanel();
JLabel mortgageLabel = new JLabel("MORTGAGE PAYMENT CALCULATOR", JLabel.CENTER);
JPanel row2 = new JPanel(new GridLayout(1, 2));
JLabel principalLabel = new JLabel("Mortgage Principal $",JLabel.LEFT);
principalTxt = new JTextField(10);
JPanel row3 = new JPanel(new GridLayout(1, 2));
JLabel termLabel = new JLabel("Mortgage Term (Yrs)",JLabel.LEFT);
termTxt = new JTextField(10);
JPanel row4 = new JPanel(new GridLayout(1, 2));
JLabel rateLabel = new JLabel("Interest Rate (%)", JLabel.LEFT);
rateTxt = new JTextField(10);
JPanel row5 = new JPanel(new GridLayout(1, 2));
JLabel presetLabel = new JLabel("Preset Term and Interest Rate:", JLabel.LEFT);
options = new JComboBox();
MessageFormat mf = new MessageFormat("{0} years at {1,number,#.##}%");
JLabel choiceLabel = new JLabel(" (choose rate)");
for (int i = 0; i < termArray.length; i++) {
options.addItem(mf.format(new Object[] { new Integer(termArray [i]),
new Double(rateArray[i])}));
}
JPanel row6 = new JPanel(new GridLayout(1, 2));
JLabel monthlyPaymentLabel = new JLabel("Monthly Payment $", JLabel.LEFT);
monthlyPaymentTxt = new JTextField(10);
//create buttons
JPanel button = new JPanel(new FlowLayout(FlowLayout.CENTER, 10, 10));
graphButton = new JButton("Display Graph");
amortizeButton = new JButton("Amortize Payments");
clearButton = new JButton("Clear");
exitButton = new JButton("Exit");
calculateButton = new JButton("Calculate");
//create textarea to display Amortize output
displayArea = new JTextArea(10, 45);
JScrollPane scroll = new JScrollPane(displayArea);
Container pane = getContentPane();
// Set layout before adding components.
pane.setLayout(new BoxLayout( pane, BoxLayout.Y_AXIS));
Border rowborder = new EmptyBorder( 3, 10, 3, 10 );
pane.add(row1);
row1.add(mortgageLabel);
row1.setMaximumSize( new Dimension( 10000, row1.getMinimumSize().height));
row1.setBorder( rowborder);
pane.add(row2);
row2.add(principalLabel);
row2.add(principalTxt);
row2.setMaximumSize( new Dimension( 10000, row2.getMinimumSize().height));
row2.setBorder( rowborder);
pane.add(row3);
row3.add(termLabel);
row3.add(termTxt);
row3.setMaximumSize( new Dimension( 10000, row3.getMinimumSize().height));
row3.setBorder( rowborder);
pane.add(row4);
row4.add(rateLabel);
row4.add(rateTxt);
row4.setMaximumSize( new Dimension( 10000, row4.getMinimumSize().height));
row4.setBorder( rowborder);
pane.add(row5);
row5.add(presetLabel);
row5.setMaximumSize( new Dimension( 10000, row4.getMinimumSize().height));
row5.setBorder( rowborder);
pane.add(row6);
row6.add(choiceLabel);
row6.setMaximumSize( new Dimension( 10000, row4.getMinimumSize().height));
row6.setBorder( rowborder);
JPanel radioPanel = new JPanel();
radioPanel.setLayout(new FlowLayout(FlowLayout.RIGHT, 4, 4 ));
radioPanel.add(options);
pane.add(radioPanel);
radioPanel.setMaximumSize( new Dimension( 10000,
radioPanel.getMinimumSize().height));
radioPanel.setBorder( rowborder);
JPanel row7 = new JPanel();
pane.add(row7);
row7.add(monthlyPaymentLabel);
row7.add(monthlyPaymentTxt);
// monthlyPaymentTxt.setEnabled(false); //set payment amount uneditable
monthlyPaymentTxt.setFocusable(false);
row7.setMaximumSize( new Dimension( 10000, row5.getMinimumSize().height));
row7.setBorder( rowborder);
//Add buttons
button.add(calculateButton);
button.add(clearButton);
button.add(exitButton);
button.add(amortizeButton);
button.add(graphButton);
pane.add(button);
button.setMaximumSize( new Dimension( 10000, button.getMinimumSize().height));
//scroll text pane for Amortize output
scroll.setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
pane.add(scroll);
setContentPane(pane);
//add listeners for buttons and combo box
options.addActionListener(this);
clearButton.addActionListener(this);
exitButton.addActionListener(this);
calculateButton.addActionListener(this);
amortizeButton.addActionListener(this);
graphButton.addActionListener(this);
// Keep JFrame method together.
setSize(550, 500);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}
public void actionPerformed(ActionEvent event) {
Object command = event.getSource();
if(command == calculateButton) { //function for Calculate button
try {
principal = Double.parseDouble(principalTxt.getText());
} catch(NumberFormatException e) {
//catch null pointer exception if Principal is null
JOptionPane.showMessageDialog(null, "Invaild Entry! Please Try Again",
"ERROR", JOptionPane.ERROR_MESSAGE);
}
try {
//Get input from Term text box, checked first before combo box
term = Integer.parseInt(termTxt.getText());
rate = Double.parseDouble(rateTxt.getText()); //Input from Rate text box
} catch(NumberFormatException e) {
//If Term and Rate are null, buttons are checked for input values
//Set rate and term based on which item in the combobox is selected
//Still have to fill in this area for the combo box arrays
//If no option is selected and combo box null,
// this is an actual error.
JOptionPane.showMessageDialog(null, "Invaild Entry! " +
"Please Try Again",
"ERROR", JOptionPane.ERROR_MESSAGE);
}
interest = rate / 100 / 12; //Monthly interst rate
notePeriod = term * 12; //Number of months over which loan is amortized
//calculation formula
monthlyPayment = (principal * interest) /
(1 - Math.pow(1 + interest, -notePeriod));
monthlyPaymentTxt.setText("" + df.format(monthlyPayment));
}
if(command == clearButton) { //Function for Clear button
principalTxt.setText("");
monthlyPaymentTxt.setText("");
rateTxt.setText("");
termTxt.setText("");
displayArea.setText("");
}
if(command == exitButton) { //Function for Exit button
System.exit(0);
}
if (command == amortizeButton) { //Function for Amortize button
//Amoritization variables
double loanBalance = notePeriod * monthlyPayment;
// You need to use the member variables with these two names
// so you can send them to your GraphPanel. Instantiate them
// here and fill the elements in this loop. The member
// variables remain null and choke up GraphPanel.
double interestPaid = 0; //Interest paid on the loan
double monthlyPrincipal = 0; //Principal in each monthly payment
//running total of principal after payment
double principalBalance = principal;
//String for output
String titles = "Month\t Principal\t\tInterest\t\tBalance\n";
displayArea.setText(titles);
displayArea.append(""); //Inserts a blank line
interestAmts = new float[term*12];
principalAmts = new float[term*12];
//This loop is used to calculate and display the payment schedule information
for(int counter = 0; counter < term * 12 - 0; counter++) { //start outer loop
//start inner loop
interestPaid = principalBalance * interest;
interestAmts[counter] = (float)interestPaid;
monthlyPrincipal = monthlyPayment - interestPaid;
principalAmts[counter] = (float)monthlyPrincipal;
loanBalance = loanBalance - monthlyPayment;
principalBalance = principalBalance - monthlyPrincipal;
//formatting for output
displayArea.setCaretPosition(0);
displayArea.append((counter +1) + ")\t" +
df.format(monthlyPrincipal)+"\t\t" +
df.format(interestPaid)+"\t\t" +
df.format(principalBalance)+"\n");
}
}
if (command == graphButton) { //Function for Graph button
JDialog d = new JDialog(this, false);
d.getContentPane().add(new GraphPanel(principalAmts, interestAmts));
d.setSize(800,600);
d.setLocation(200,100);
d.setVisible(true);
}
}
//reading from sequential file
private void load() {
Reader fis;
try {
fis = new InputStreamReader(getClass().getResourceAsStream("data.txt"));
BufferedReader br = new BufferedReader( fis );
termArray = new int[4];
rateArray = new double[4];
String line;
int i = 0;
while((line = br.readLine()) != null) {
String[] s = line.split(",");
termArray[ i ] = Integer.parseInt(s[0].trim());
rateArray[ i ] = Double.parseDouble(s[1].trim());
i++;
}
br.close();
} catch ( Exception e1 ) {
e1.printStackTrace( );
}
}
public static void main(String[] args) {
MC smc = new MC();
}
}