import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;

public class MortgageWindow
{
   public static void main(String args[])
   {
      Frame f = new MyFrame();
      f.show();
   }
}



class MyFrame extends Frame implements TextListener {

   TextField principalField = new TextField("0.00", 15),
             rateField = new TextField("0.00", 6),
             yearsField = new TextField("0", 3),
             paymentField = new TextField("0.00", 15);
   double principal, rate, ratePercent;
   int years, n;
   final int paymentsPerYear = 12;
   final int timesPerYearCalculated = 12;
   double effectiveAnnualRate;
   double payment;

   public MyFrame()
   {
      setTitle("Mortgage Payment Calculator");
      setLayout(new GridLayout(4,2));

      Label principalLabel = new Label("Principal $"),
            rateLabel = new Label("Rate (%)"),
            yearsLabel = new Label("Years"),
            paymentLabel = new Label("Payment $");
      Panel principalLabelPanel = new Panel(new FlowLayout(FlowLayout.RIGHT)),
            rateLabelPanel = new Panel(new FlowLayout(FlowLayout.RIGHT)),
            yearsLabelPanel = new Panel(new FlowLayout(FlowLayout.RIGHT)),
            paymentLabelPanel = new Panel(new FlowLayout(FlowLayout.RIGHT));
      Panel principalFieldPanel = new Panel(new FlowLayout(FlowLayout.LEFT)),
            rateFieldPanel = new Panel(new FlowLayout(FlowLayout.LEFT)),
            yearsFieldPanel = new Panel(new FlowLayout(FlowLayout.LEFT)),
            paymentFieldPanel = new Panel(new FlowLayout(FlowLayout.LEFT));



      principalLabelPanel.add(principalLabel);
      principalFieldPanel.add(principalField);
      rateLabelPanel.add(rateLabel);
      rateFieldPanel.add(rateField);
      yearsLabelPanel.add(yearsLabel);
      yearsFieldPanel.add(yearsField);
      paymentLabelPanel.add(paymentLabel);
      paymentFieldPanel.add(paymentField);
      add(principalLabelPanel);
      add(principalFieldPanel);
      add(rateLabelPanel);
      add(rateFieldPanel);
      add(yearsLabelPanel);
      add(yearsFieldPanel);
      add(paymentLabelPanel);
      add(paymentFieldPanel);

      principalField.addTextListener(this);
      rateField.addTextListener(this);
      yearsField.addTextListener(this);
      addWindowListener(new MyAdapter(this));

      pack();
      show();

   }

   DecimalFormat currency = new DecimalFormat("####0.00");

   public void textValueChanged (TextEvent e)
   {
      Object source=e.getSource();
      if (source == principalField ||
          source == rateField ||
          source == yearsField)
      {
         try
         {
            principal = Double.parseDouble(principalField.getText());
            ratePercent = Double.parseDouble(rateField.getText());
            rate = ratePercent/100.0;
            years = Integer.parseInt(yearsField.getText());

            n = paymentsPerYear * years;
            effectiveAnnualRate = rate / paymentsPerYear;
            payment = principal*(effectiveAnnualRate / (1 - Math.pow(1 + effectiveAnnualRate, -n)));

            paymentField.setText(currency.format(payment));
         }
         catch (NumberFormatException ex) {}
      }
   }
}

class MyAdapter extends WindowAdapter {

  Frame myFrame;
  MyAdapter(Frame f) {
    super();
    myFrame = f;
  }

  public void windowClosing(WindowEvent e)
  {
    myFrame.dispose();
  }
}