InterestApplet.java

//Import all required Packages
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableColumn;
import java.awt.*;
import java.text.*;
import java.awt.event.*;


public class InterestApplet extends JApplet implements ActionListener {

    JPanel row1;
    JLabel lblAmount;
    JTextField txtAmount;
    JLabel lblInterest;
    JTextField txtInterest;
    JLabel lblTerm;
    JTextField txtTerm;

    JPanel row2;
    JTable resultsTable;
    JScrollPane textPane;

    JPanel row3;
    JButton calculateButton;
    JButton clearButton;
    JButton exitButton;


    public void init()
    {
        //Build GUI
        setSize(1024, 720);

        // row1
        row1 = new JPanel();

        lblAmount = new JLabel(" Mortgage: $", JLabel.LEFT);
        txtAmount = new JTextField(10);

        lblInterest = new JLabel("Interest %", JLabel.LEFT);
        txtInterest = new JTextField(6);

        lblTerm = new JLabel("Term in Years", JLabel.LEFT);
        txtTerm = new JTextField(6);

        row1.add(lblAmount);
        row1.add(txtAmount);
        row1.add(lblInterest);
        row1.add(txtInterest);
        row1.add(lblTerm);
        row1.add(txtTerm);

        // row2
        row2 = new JPanel(new BorderLayout());
        DefaultTableModel model = CreateTableModel();
        resultsTable = new JTable(model);
        textPane = new JScrollPane(resultsTable);
        textPane.setPreferredSize(new Dimension(610,200));
        row2.add(textPane,BorderLayout.CENTER);

        //row 3
        row3 = new JPanel(new GridLayout(1,3,75,1));

        calculateButton = new JButton("Calculate");
        clearButton = new JButton("Clear");
        exitButton = new JButton("Exit");

        //Create Calculate button and add listener
        calculateButton.addActionListener(this);
        clearButton.addActionListener(this);
        exitButton.addActionListener(this);

        row3.add(exitButton);
        row3.add(clearButton);
        row3.add(calculateButton);
        getContentPane().add(row1,BorderLayout.NORTH);
        getContentPane().add(row2,BorderLayout.CENTER);
        getContentPane().add(row3,BorderLayout.SOUTH);
    }

    //Define actions performed for buttons
    public void actionPerformed(ActionEvent e)
    {
        if (e.getSource() == calculateButton)
        {
            Double userAmount = Double.parseDouble(txtAmount.getText());
            Double userInterest = Double.parseDouble(txtInterest.getText());
            Integer userTerm = Integer.parseInt(txtTerm.getText());
            CalculateMonthlyPayment(userAmount, userInterest, userTerm);
        }
        if (e.getSource() == clearButton){
            DefaultTableModel model = CreateTableModel();
            resultsTable.setModel(model);
            txtAmount.setText("");
            txtInterest.setText("");
            txtTerm.setText("");
        }
        if (e.getSource() == exitButton){
            setVisible(false);
            System.exit(0);
        }
    }


    private void addRow(int payment, double amount, double interest, double principal, double balance)
    {
        DefaultTableModel model = (DefaultTableModel)resultsTable.getModel();
        model.addRow(new Object[]{
                String.format("%s", payment),
                String.format("%.2f", amount),
                String.format("%.2f", interest),
                String.format("%.2f", principal),
                String.format("%.2f", balance)
        });
    }


    private void CalculateMonthlyPayment(double p,double ir, int ny){
        double b;
        double im =(ir/12)/100;
        int nm = ny*12;
        double r,t,a;
        int i;

        r=p*im*Math.pow(1+im,(double)nm)/(Math.pow(1+im,(double)nm)-1);

        //print amortization schedule for all months except the last month
        for(i=1;i<nm;i++){
            t = p*im;//interest paid
            a = r-t; //principal paid
            b = p-a; //new balance
            addRow(i, r, t, a, b);
            p = b;  //update old balance
        }
        //last month
        a = p;
        t = p*im;
        r = a+t;
        b = 0.0;
        addRow(i, r, t, a, b);

    }

    private DefaultTableModel CreateTableModel(){
        DefaultTableModel model = new DefaultTableModel();
        model.addColumn("Payment");
        model.addColumn("Monthly Payment");
        model.addColumn("Interest Payment");
        model.addColumn("Principal Payment");
        model.addColumn("Balance");
        return model;
    }
}