1  import java.awt.event.ActionEvent;

  2  import java.awt.event.ActionListener;

  3  import javax.swing.JButton;

  4  import javax.swing.JFrame;

  5  import javax.swing.JLabel;

  6  import javax.swing.JPanel;

  7  import javax.swing.JScrollPane;

  8  import javax.swing.JTextArea;

  9  import javax.swing.JTextField;

 10  

 11  /**

 12     A frame that shows the growth of an investment with variable interest,

 13     using a text area.

 14  */

 15  public class InvestmentFrame3 extends JFrame

 16  {

 17     private static final int FRAME_WIDTH = 400;

 18     private static final int FRAME_HEIGHT = 250;

 19     

 20     private static final int AREA_ROWS = 10;

 21     private static final int AREA_COLUMNS = 30;

 22  

 23     private static final double DEFAULT_RATE = 5;

 24     private static final double INITIAL_BALANCE = 1000;   

 25       

 26     private JLabel rateLabel;

 27     private JTextField rateField;

 28     private JButton button;

 29     private JTextArea resultArea;

 30     private double balance;

 31   

 32     public InvestmentFrame3()

 33     {  

 34        balance = INITIAL_BALANCE;

 35        resultArea = new JTextArea(AREA_ROWS, AREA_COLUMNS);

 36        resultArea.setText(balance + "\n");

 37        resultArea.setEditable(false);

 38              

 39        createTextField();

 40        createButton();

 41        createPanel();

 42  

 43        setSize(FRAME_WIDTH, FRAME_HEIGHT);

 44     }

 45  

 46     private void createTextField()

 47     {

 48        rateLabel = new JLabel("Interest Rate: ");

 49  

 50        final int FIELD_WIDTH = 10;

 51        rateField = new JTextField(FIELD_WIDTH);

 52        rateField.setText("" + DEFAULT_RATE);

 53     }

 54     

 55     class AddInterestListener implements ActionListener

 56     {

 57        public void actionPerformed(ActionEvent event)

 58        {

 59           double rate = Double.parseDouble(rateField.getText());

 60           double interest = balance * rate / 100;

 61           balance = balance + interest;

 62           resultArea.append(balance + "\n");

 63        }            

 64     }

 65  

 66     private void createButton()

 67     {

 68        button = new JButton("Add Interest");      

 69        

 70        ActionListener listener = new AddInterestListener();

 71        button.addActionListener(listener);

 72     }

 73  

 74     private void createPanel()

 75     {

 76        JPanel panel = new JPanel();

 77        panel.add(rateLabel);

 78        panel.add(rateField);

 79        panel.add(button);

 80        JScrollPane scrollPane = new JScrollPane(resultArea);

 81        panel.add(scrollPane);      

 82        add(panel);

 83     }

 84  }