November 4th, 2013
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
/**
This program demonstrates how to install an action listener.
*/
public class ButtonViewer
{
private static final int FRAME_WIDTH = 100;
private static final int FRAME_HEIGHT = 60;
public static void main(String[] args)
{
JFrame frame = new JFrame();
JButton button = new JButton("Click me!");
frame.add(button);
ActionListener listener = new ClickListener();
button.addActionListener(listener);
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
/**
An action listener that prints a message.
*/
public class ClickListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
System.out.println("I was clicked.");
}
}
/**
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;
/**
This program demonstrates how an action listener can access
a variable from a surrounding block.
*/
public class InvestmentViewer1
{
private static final int FRAME_WIDTH = 120;
private static final int FRAME_HEIGHT = 60;
private static final double INTEREST_RATE = 10;
private static final double INITIAL_BALANCE = 1000;
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);
}
}
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;
/**
This program displays the growth of an investment.
*/
public class InvestmentViewer2
{
private static final int FRAME_WIDTH = 400;
private static final int FRAME_HEIGHT = 100;
private static final double INTEREST_RATE = 10;
private static final double INITIAL_BALANCE = 1000;
public static void main(String[] args)
{
JFrame frame = new JFrame();
// The button to trigger the calculation
JButton button = new JButton("Add Interest");
// The application adds interest to this bank account
final BankAccount account = new BankAccount(INITIAL_BALANCE);
// The label for displaying the results
final JLabel label = new JLabel("balance: " + account.getBalance());
// The panel that holds the user interface components
JPanel panel = new JPanel();
panel.add(button);
panel.add(label);
frame.add(panel);
class AddInterestListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
double interest = account.getBalance() * INTEREST_RATE / 100;
account.deposit(interest);
label.setText("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);
}
}
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import javax.swing.JComponent;
/**
This component displays a rectangle that can be moved.
*/
public class RectangleComponent extends JComponent
{
private static final int BOX_X = 100;
private static final int BOX_Y = 100;
private static final int BOX_WIDTH = 20;
private static final int BOX_HEIGHT = 30;
private Rectangle box;
public RectangleComponent()
{
// The rectangle that the paintComponent method draws
box = new Rectangle(BOX_X, BOX_Y, BOX_WIDTH, BOX_HEIGHT);
}
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D) g;
g2.draw(box);
}
/**
Moves the rectangle to the given location.
@param x the x-position of the new location
@param y the y-position of the new location
*/
public void moveTo(int x, int y)
{
box.setLocation(x, y);
repaint();
}
}
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
/**
This program displays a RectangleComponent.
*/
public class RectangleComponentViewer
{
private static final int FRAME_WIDTH = 300;
private static final int FRAME_HEIGHT = 400;
public static void main(String[] args)
{
final RectangleComponent component = new RectangleComponent();
// Add mouse press listener
class MousePressListener implements MouseListener
{
public void mousePressed(MouseEvent event)
{
int x = event.getX();
int y = event.getY();
component.moveTo(x, y);
}
// Do-nothing methods
public void mouseReleased(MouseEvent event) {}
public void mouseClicked(MouseEvent event) {}
public void mouseEntered(MouseEvent event) {}
public void mouseExited(MouseEvent event) {}
}
MouseListener listener = new MousePressListener();
component.addMouseListener(listener);
JFrame frame = new JFrame();
frame.add(component);
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import javax.swing.JComponent;
/**
This component displays a rectangle that can be moved.
*/
public class RectangleComponent extends JComponent
{
private static final int BOX_X = 100;
private static final int BOX_Y = 100;
private static final int BOX_WIDTH = 20;
private static final int BOX_HEIGHT = 30;
private Rectangle box;
public RectangleComponent()
{
// The rectangle that the paintComponent method draws
box = new Rectangle(BOX_X, BOX_Y, BOX_WIDTH, BOX_HEIGHT);
}
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D) g;
g2.draw(box);
}
/**
Moves the rectangle by a given amount.
@param x the amount to move in the x-direction
@param y the amount to move in the y-direction
*/
public void moveBy(int dx, int dy)
{
box.translate(dx, dy);
repaint();
}
}
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.Timer;
/**
This program moves the rectangle.
*/
public class RectangleMover
{
private static final int FRAME_WIDTH = 300;
private static final int FRAME_HEIGHT = 400;
public static void main(String[] args)
{
JFrame frame = new JFrame();
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setTitle("An animated rectangle");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final RectangleComponent component = new RectangleComponent();
frame.add(component);
frame.setVisible(true);
class TimerListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
component.moveBy(1, 1);
}
}
ActionListener listener = new TimerListener();
final int DELAY = 100; // Milliseconds between timer ticks
Timer t = new Timer(DELAY, listener);
t.start();
}
}
Homework: Exercise 4: Enhance the ButtonViewer program so that it prints a message “I was clicked n times!” whenever the button is clicked. The value n should be incremented with each click.
