November 11th, 2014

How to put some components together:
This application uses JTextField, JButton and JLabel

/**
   A bank account has a balance that can be changed by 
   deposits and withdrawals.
*/
public class BankAccount
{  
   private double balance;

   /**
      Constructs a bank account with a zero balance.
   */
   public BankAccount()
   {   
      balance = 0;
   }

   /**
      Constructs a bank account with a given balance.
      @param initialBalance the initial balance
   */
   public BankAccount(double initialBalance)
   {   
      balance = initialBalance;
   }

   /**
      Deposits money into the bank account.
      @param amount the amount to deposit
   */
   public void deposit(double amount)
   {  
      double newBalance = balance + amount;
      balance = newBalance;
   }

   /**
      Withdraws money from the bank account.
      @param amount the amount to withdraw
   */
   public void withdraw(double amount)
   {   
      double newBalance = balance - amount;
      balance = newBalance;
   }

   /**
      Gets the current balance of the bank account.
      @return the current balance
   */
   public double getBalance()
   {   
      return balance;
   }
}

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

/**
   A frame that shows the growth of an investment with variable interest.
*/
public class InvestmentFrame extends JFrame
{    
   private static final int FRAME_WIDTH = 450;
   private static final int FRAME_HEIGHT = 100;

   private static final double DEFAULT_RATE = 5;
   private static final double INITIAL_BALANCE = 1000;   

   private JLabel rateLabel;
   private JTextField rateField;
   private JButton button;
   private JLabel resultLabel;
   private JPanel panel;
   private BankAccount account;
 
   public InvestmentFrame()
   {  
      account = new BankAccount(INITIAL_BALANCE);

      // Use instance variables for components 
      resultLabel = new JLabel("balance: " + account.getBalance());

      // Use helper methods 
      createTextField();
      createButton();
      createPanel();

      setSize(FRAME_WIDTH, FRAME_HEIGHT);
   }

   private void createTextField()
   {
      rateLabel = new JLabel("Interest Rate: ");

      final int FIELD_WIDTH = 10;
      rateField = new JTextField(FIELD_WIDTH);
      rateField.setText("" + DEFAULT_RATE);
   }
   
   private void createButton()
   {
      button = new JButton("Add Interest");
      
      class AddInterestListener implements ActionListener
      {
         public void actionPerformed(ActionEvent event)
         {
            double rate = Double.parseDouble(rateField.getText());
            double interest = account.getBalance() * rate / 100;
            account.deposit(interest);
            resultLabel.setText("balance: " + account.getBalance());
         }            
      }
      
      ActionListener listener = new AddInterestListener();
      button.addActionListener(listener);
   }

   private void createPanel()
   {
      panel = new JPanel();
      panel.add(rateLabel);
      panel.add(rateField);
      panel.add(button);
      panel.add(resultLabel);      
      add(panel);
   } 
}

import javax.swing.JFrame;

/**
   This program displays the growth of an investment. 
*/
public class InvestmentViewer3
{  
   public static void main(String[] args)
   {  
      JFrame frame = new InvestmentFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
   }
}