Thread: Interest calculator applet

Sorry to bother everyone but I'm having an issue trying to find or help myself with the code to implement calculating interest. Basically a user has to be able to input loan amount/interest %/ terms of the loan and loan payments. My issue is the code for calculating the interest. Here is what i have so far.

import javax.swing.*;
import java.awt.*;
import java.text.*;
import java.awt.event.*;
 
 
public class SchoolApplet8 extends JApplet implements ActionListener {
 
 
	double userAmount;
	double userInterest;
	double userTerm;
 
 
	int month = 0;
	double remainBalance = 0;
	double interestPayment = 0;
	double principalPaid = 0;
 
	JPanel row1;
	JLabel lblAmount;
	JTextField txtAmount;
	JLabel lblInterest;
	JTextField txtInterest;
	JLabel lblTerm;
	JTextField txtTerm;
	JLabel lblMonthlyPayments;
	JTextField txtMonthlyPayments;
	JLabel lblPayment;
	JTextField txtPayment;
 
	JPanel row2;
	JLabel lblHeader;
	JTextArea txtResults;
	JScrollPane textPane;
 
 
	JPanel row3;
	JButton calculateButton;
	JButton clearButton;
	JButton exitButton;
 
 
 
	public void init()
	{
 
 
 
	//Instantiate GUI Components
 
	// row1
	row1 = new JPanel();
 
	lblAmount = new JLabel(" Loan Amount: $", JLabel.LEFT);
	txtAmount = new JTextField(10);
 
	lblMonthlyPayments =  new JLabel("Monthly Payments", JLabel.LEFT);
	txtMonthlyPayments =  new JTextField(6);
 
 
	lblInterest = new JLabel("Interest Per Period %", JLabel.LEFT);
	txtInterest = new JTextField(6);
 
	lblTerm = new JLabel("Term in Years", JLabel.LEFT);
	txtTerm = new JTextField(6);
 
 
 
	// TO DO
	// create a new JLabel and assign it to lblPayment
	// create a new JTextField(10) and assign it to txtPayment
 
 
 
	// row2
	row2 = new JPanel(new BorderLayout());
 
	String pad = "                             ";
	lblHeader = new JLabel("Payment #"+pad+"Monthly Payment Amount:"+pad+"Interest Paid:"+pad+"Principal"+pad+"Balance:");
 
	txtResults = new JTextArea(10, 53);
	textPane = new JScrollPane(txtResults);
 
 
 
	//row 3
	row3 = new JPanel(new GridLayout(1,3,75,1));
 
	calculateButton = new JButton("Calculate");
	clearButton = new JButton("Clear");
	exitButton = new JButton("Exit");
 
 
 
	//Build GUI
 
	setSize(600, 250);
 
 
	row1.add(lblAmount);
	row1.add(txtAmount);
 
	row1.add(lblMonthlyPayments);
	row1.add(txtMonthlyPayments);
 
	row1.add(lblInterest);
	row1.add(txtInterest);
 
	row1.add(lblTerm);
	row1.add(txtTerm);
 
 
 
 
	// To DO
	// add lblPayment & txtPayment to row1
	// set editable of txtPayment to false: txtPayment.setEditable(false);
	//
 
 
 
	textPane.setPreferredSize(new Dimension(610,200));
	row2.add(lblHeader,BorderLayout.NORTH);
	row2.add(textPane,BorderLayout.CENTER);
 
 
 
	//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 balance = 0;
			double monthPayment=0;
 
 
 
			userAmount = Double.parseDouble(txtAmount.getText());
 
			userInterest = Double.parseDouble(txtInterest.getText());
 
			userTerm = Double.parseDouble(txtTerm.getText());
 
 
 
			//formats answer in currency format then to string format for display
			NumberFormat fmt = NumberFormat.getCurrencyInstance();
			monthPayment = CalculateMonthlyPayment();
			String payment = fmt.format(monthPayment);
 
			// TO DO
			// Display payment in txtPayment : txtPayment.setText(" "+ payment);
			//
 
 
 
			balance = userAmount;
			month = (int)userTerm * 12;
 
			for(int index = 1; index <= month ; index++)
				{
				interestPayment = balance * (userInterest * .01/12);
				principalPaid = monthPayment - interestPayment;
				remainBalance = balance - principalPaid;
 
 
				txtResults.append(" " + index + "\t\t "+ fmt.format(balance) + "\t\t"
				+ fmt.format(interestPayment) + "\t\t"  + fmt.format(remainBalance) + "\n");
 
				balance = remainBalance;
				}
 
 
		}
 
		else if (e.getSource() == clearButton)
		{
			txtAmount.setText(null);
			txtPayment.setText(null);
			txtResults.setText(null);
		}
 
		else if (e.getSource() == exitButton)
		{
			System.exit(0);
		}
	}
 
 
	//Mortgage Payment Calculations
	double CalculateMonthlyPayment()
	{
 
		return (userAmount * ((1 + (userInterest*.01)/12)-1) / (1-(Math.pow((1+(userInterest*.01)/12),-(userTerm*12)))));
 
	}
 
 
 
}

Any help would greatly be appreciated Thanks

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You said you're having problems calculating the interest. What kind of problems are you having? Are you getting a compiler error? Incorrect results? The more info you provide the easier it is for us to help you. If you have a compile error, please post the error message.


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Also posted at java applet | DaniWeb