A sample interest calculator, very basic in functionality, coded in Java and ready to be compiled and executed as a Java Applet.

1.import java.awt.*;
2.import java.awt.event.*;
3.import java.applet.*;
4.import java.text.NumberFormat;
5. 
6.public class InterestCalculator extends Applet implements ActionListener
7.{
8.        TextField textPresentVal = new TextField("0", 10);
9.        TextField textInterestRate = new TextField("0", 10);
10.        TextField textPeriods = new TextField("0", 10);
11.        Label lblPresentVal = new Label("Present Value");
12.        Label lblInterestRate = new Label("Interest Rate");
13.        Label lblPeriods = new Label("Number of Periods");
14.        Label lblFutureVal = new Label("Future Value:");
15.        Button btnOk = new Button("Calculate");
16. 
17.        public void init()
18.        {
19. 
20.                add(lblPresentVal);
21.                add(textPresentVal);
22.                add(lblInterestRate);
23.                add(textInterestRate);
24.                add(lblPeriods);
25.                add(textPeriods);
26.                add(lblFutureVal);
27.                add(btnOk);
28. 
29.                btnOk.addActionListener(this);
30.       }
31. 
32.        public void actionPerformed(ActionEvent evt)  
33.        {
34.            if (evt.getSource() == btnOk)
35.           {
36.                int PresentVal = Integer.parseInt(textPresentVal.getText());
37.                int InterestRate = Integer.parseInt(textInterestRate.getText());
38.                int Periods = Integer.parseInt(textPeriods.getText());
39.                double FutureVal = PresentVal * (Math.pow((1 + InterestRate), Periods));
40.               NumberFormat nf = NumberFormat.getCurrencyInstance();
41.                lblTotal.setText("Future Value: " + nf.format(FutureVal));
42. 
43.                repaint();
44.            }
45.        }
46.}