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);
}
}
