InvestmentViewer1.java

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;

/**
   This program demonstrates how an action listener can access 
   a variable from a surrounding block.
*/
public class InvestmentViewer1
{  
   public static void main(String[] args)
   {  
      JFrame frame = new JFrame();

      // The button to trigger the calculation
      JButton button = new JButton("Add Interest");
      frame.add(button);

      // The application adds interest to this bank account
      final BankAccount account = new BankAccount(INITIAL_BALANCE);
      
      class AddInterestListener implements ActionListener
      {
         public void actionPerformed(ActionEvent event)
         {
            // The listener method accesses the account variable
            // from the surrounding block
            double interest = account.getBalance() 
                  * INTEREST_RATE / 100;
            account.deposit(interest);
            System.out.println("balance: " + account.getBalance());
         }            
      }
     
      ActionListener listener = new AddInterestListener();
      button.addActionListener(listener);

      frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
   }

   private static final double INTEREST_RATE = 10;
   private static final double INITIAL_BALANCE = 1000;

   private static final int FRAME_WIDTH = 120;
   private static final int FRAME_HEIGHT = 60;
}