LoanBalance.java

// Find the remaining balance on a loan.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
/*
  <applet code="RemBal" width=340 height=260>
</applet> */
public class RemBal extends JApplet
  implements ActionListener {
  JTextField orgPText, paymentText, remBalText,
             rateText, numPayText;
  JButton doIt;
  double orgPrincipal; // original principal
  double intRate;      // interest rate
  double payment;      // amount of each payment
  double numPayments;  // number of payments made
  /* Number of payments per year. You could
     allow this value to be set by the user. */
  final int payPerYear = 12;
  NumberFormat nf;
  public void init() {
    try {
      SwingUtilities.invokeAndWait(new Runnable () {
        public void run() {
          makeGUI(); // initialize the GUI
        }
      });
    } catch(Exception exc) {
System.out.println("Can't create because of "+ exc);
} }
// Set up and initialize the GUI.
private void makeGUI() {
  // Use a grid bag layout.
  GridBagLayout gbag = new GridBagLayout();
  GridBagConstraints gbc = new GridBagConstraints();
  setLayout(gbag);
  JLabel heading = new
         JLabel("Find Loan Balance ");
  JLabel orgPLab = new JLabel("Original Principal ");
  JLabel paymentLab = new JLabel("Amount of Payment ");
  JLabel numPayLab = new JLabel("Number of Payments Made ");
  JLabel rateLab = new JLabel("Interest Rate ");
  JLabel remBalLab = new JLabel("Remaining Balance ");
  orgPText = new JTextField(10);
  paymentText = new JTextField(10);
  remBalText = new JTextField(10);
  rateText = new JTextField(10);
  numPayText = new JTextField(10);
  // Payment field for display only.
  remBalText.setEditable(false);
  doIt = new JButton("Compute");
  // Define the grid bag.
   gbc.weighty = 1.0; // use a row weight of 1
  gbc.gridwidth = GridBagConstraints.REMAINDER;
  gbc.anchor = GridBagConstraints.NORTH;
  gbag.setConstraints(heading, gbc);
  // Anchor most components to the right.
  gbc.anchor = GridBagConstraints.EAST;
  gbc.gridwidth = GridBagConstraints.RELATIVE;
  gbag.setConstraints(orgPLab, gbc);
  gbc.gridwidth = GridBagConstraints.REMAINDER;
  gbag.setConstraints(orgPText, gbc);
  gbc.gridwidth = GridBagConstraints.RELATIVE;
  gbag.setConstraints(paymentLab, gbc);
  gbc.gridwidth = GridBagConstraints.REMAINDER;
  gbag.setConstraints(paymentText, gbc);
  gbc.gridwidth = GridBagConstraints.RELATIVE;
  gbag.setConstraints(rateLab, gbc);
  gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(rateText, gbc);
gbc.gridwidth = GridBagConstraints.RELATIVE;
gbag.setConstraints(numPayLab, gbc);
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(numPayText, gbc);
gbc.gridwidth = GridBagConstraints.RELATIVE;
gbag.setConstraints(remBalLab, gbc);
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(remBalText, gbc);
gbc.anchor = GridBagConstraints.CENTER;
gbag.setConstraints(doIt, gbc);
// Add all the components.
add(heading);
add(orgPLab);
add(orgPText);
add(paymentLab);
add(paymentText);
add(numPayLab);
add(numPayText);
add(rateLab);
add(rateText);
add(remBalLab);
add(remBalText);
add(doIt);
// Register to receive action events.
orgPText.addActionListener(this);
numPayText.addActionListener(this);
rateText.addActionListener(this);
paymentText.addActionListener(this);
doIt.addActionListener(this);
// Create a number format.
nf = NumberFormat.getInstance();
nf.setMinimumFractionDigits(2);
nf.setMaximumFractionDigits(2);
}
/* User pressed Enter on a text field
   or pressed Compute. Display the result if all
   fields are completed. */
public void actionPerformed(ActionEvent ae) {
  double result = 0.0;
  String orgPStr = orgPText.getText();
  String numPayStr = numPayText.getText();
  String rateStr = rateText.getText();
  String payStr = paymentText.getText();
         try {
           if(orgPStr.length() != 0 &&
              numPayStr.length() != 0 &&
              rateStr.length() != 0 &&
              payStr.length() != 0) {
             orgPrincipal = Double.parseDouble(orgPStr);
             numPayments = Double.parseDouble(numPayStr);
             intRate = Double.parseDouble(rateStr) / 100;
             payment = Double.parseDouble(payStr);
             result = compute();
             remBalText.setText(nf.format(result));
           }
           showStatus(""); // erase any previous error message
         } catch (NumberFormatException exc) {
           showStatus("Invalid Data");
           remBalText.setText("");
         }
}
       // Compute the loan balance.
       double compute() {
         double bal = orgPrincipal;
         double rate = intRate / payPerYear;
         for(int i = 0; i < numPayments; i++)
           bal -= payment - (bal * rate);
return bal; }
}








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