Really need application help

Question

OK, so I need to create an application that calculates and displays a monthly mortgage payment, and also displays the loan balance, principle applied, and interest applied for each payment over the course of the loan. The loan amount will be determined by user input, and the terms are static and will be chosen by the user, which I'd like to present in the form of radio buttons. I understand how to create the arrays and loops and everything, but I just don't understand how to implement that into an application (not an applet) and have it use a GUI. I'm also getting errors because I'm using extends Frame instead of extends JApplet, and I'm using the getContentPane method, which isn't working. It compiles fine, but I get an error when I run it. Not sure how to create the panel and stuff to put all of my components on, if I can't use JApplet right? Because it can't be an applet. Anyway, here's my code right now, any suggestions would be appreciated, or if you know of any good websites to visit that could help me with all of this. Thanks.
import java.text.*;  //importing necessary classes
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.lang.*;
//Mortgage Payment Calculator
//Version 2.0
//Written by Ryane Helder
//This program will calculate the monthly loan payment, requiring
//user input for the loan amount.  The user will then choose one of
//three loan terms to use in their calculations.  This program will
//also display the loan balance, principle applied, and interest
//applied for each month for the duration of the loan.public class Mortgage2 extends Frame implements ActionListener
     JLabel Calculator = new
     JLabel ("Mortgage Payment Calculator");
     JLabel CalculateLoan = new JLabel("This program will display information about a loan of your choice.");
     JLabel UserOption = new JLabel("You will need to input the amount of the loan.");
     JLabel ClickButton = new JLabel("Then, choose the terms of the loan, and your results will display on the screen.");
     JRadioButton FirstChoice = new JRadioButton("7 years at 5.35%");
     JRadioButton SecondChoice = new JRadioButton("15 years at 5.5%");
     JRadioButton ThirdChoice = new JRadioButton("30 years at 5.75%");
     JButton MonthlyPayment = new JButton("Calculate!");
     JButton StartOver = new JButton("Clear");
     JButton EndProgram = new JButton("Quit");
     Font bigFont = new Font("Times New Roman", Font.BOLD, 24); //create font for header
     DecimalFormat cformat = new DecimalFormat("$" + "###,###,###.##"); //format numbers to currency
public void init()
     Container con = getContentPane(); //create new Container
     con.setLayout(new FlowLayout()); //create new Layout
     Calculator.setFont(bigFont); //set font for header
     con.add(Calculator); //adding components
     con.add(CalculateLoan);
     con.add(UserOption);
     con.add(ClickButton);
     con.add(FirstChoice);
     con.add(SecondChoice);
     con.add(ThirdChoice);
     con.add(MonthlyPayment);
     con.add(StartOver);
     con.add(EndProgram);
     MonthlyPayment.addActionListener(this); //adding Listener to buttons
     StartOver.addActionListener(this);
     EndProgram.addActionListener(this);
public void actionPerformed(ActionEvent e)
     Object source = e.getSource(); //request user input
     if (source == MonthlyPayment) //if they click the button
          double amount = 0;
          double balance;
          double interest = 0;
          double principle = 0;
          int i = 0;
          int[] term = {7, 15, 30};
          double[] rate = {.0535, .055, .0575};
          double payment;
          payment = (amount*(rate/12))/(1-(Math.pow(1/(1+(rate[i]/12)),(term[i]*12)))); //formula for payment calculation
          CalculateLoan.setText("Your monthly payment will be " + cformat.format(payment)); //output to user
          } //end if statement
     } //end actionPerformed
} //end program

Answer 1

Well it�s a question of design more than anything else try using MVC pattern (more like learn it). Design the logic of your application as a separate reusable set of classes (may be you can define it in a separate package) test each component of the programme logic by using short command line test programmes. Design a way for the programme logic to communicate with a abstract GUI class this can be either by designing listeners, defining interfaces, or just a simple data structure, or an existing data structure such as TableModel (this is known as the Model in the MVC pattern). You should be able to implement your abstract GUI class as a swing interface and/or applet and/or JSP page etcetera.