1  import java.awt.event.ActionEvent;

  2  import java.awt.event.ActionListener;

  3  import javax.swing.JButton;

  4  import javax.swing.JFrame;

  5  

  6  /**

  7     This program demonstrates how an action listener can access 

  8     a variable from a surrounding block.

  9  */

 10  public class InvestmentViewer1

 11  {  

 12     private static final int FRAME_WIDTH = 120;

 13     private static final int FRAME_HEIGHT = 60;

 14  

 15     private static final double INTEREST_RATE = 10;

 16     private static final double INITIAL_BALANCE = 1000;

 17  

 18     public static void main(String[] args)

 19     {  

 20        JFrame frame = new JFrame();

 21  

 22        // The button to trigger the calculation

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

 24        frame.add(button);

 25  

 26        // The application adds interest to this bank account

 27        final BankAccount account = new BankAccount(INITIAL_BALANCE);

 28        

 29        class AddInterestListener implements ActionListener

 30        {

 31           public void actionPerformed(ActionEvent event)

 32           {

 33              // The listener method accesses the account variable

 34              // from the surrounding block

 35              double interest = account.getBalance() * INTEREST_RATE / 100;

 36              account.deposit(interest);

 37              System.out.println("balance: " + account.getBalance());

 38           }            

 39        }

 40       

 41        ActionListener listener = new AddInterestListener();

 42        button.addActionListener(listener);

 43  

 44        frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);

 45        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

 46        frame.setVisible(true);

 47     }

 48  }