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Lecture Notes
CPSC 224 (Spring 2012)
Today
• Quiz 6
• Start on Java Swing
Homework
• hw5 out
Reading
• Ch 7: 281-299
• Ch 8: 323-330
S. Bowers
1 of 10
Lecture Notes
CPSC 224 (Spring 2012)
GUI programming in Java
Early versions of Java used the “AWT”
• Abstract Window Toolkit
• an API over underlying graphics support of platform (Win, Mac, Linux, etc.)
“Swing” extends AWT
• richer API
• more consistent “look and feel”
• native “look and feels”
• more widgets
S. Bowers
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Lecture Notes
CPSC 224 (Spring 2012)
JPanels
A JPanel is called either a “panel” or “pane”
• a general-purpose container for widgets
• widgets added using panel.add(widget) ... depending on layout manager
• panels are also widgets ... so can be added to panes
• basic operations:
– add(Comonent c)
– getComponent(int i)
– remove(int i)
– set the background color
– set the layout manager (more later)
– lots more!
NOTE: You are expected to look up the classes we discuss in the Java API ...
we can’t cover all the methods/uses in class
S. Bowers
3 of 10
Lecture Notes
CPSC 224 (Spring 2012)
JFrames
A JFrame is a top-level window
import javax.swing.*;
public class Lab {
public static void main(String[] args) {
JFrame f = new JFrame("Test");
f.setSize(300, 300);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
}
}
• set/get the size
• set/get the window title
• add widgets to the “content” pane
• add/set the menu bar
• and so on
JFrame anatomy:
• root pane manages the interior of the pane (the other panes)
• layered pane for puting widgets on top of or behind other widgets
• menu bar (optional) is for menu items (File → Save, Edit → Copy, etc.)
• content pane is the visible widgets of the frame, panes added using frame.add(...)
• glass pane is used to intercept events before the content pane
S. Bowers
4 of 10
Lecture Notes
CPSC 224 (Spring 2012)
Example Widgets: JTextArea
Used for getting/displaying multiple lines of text
import javax.swing.*;
public class Lab {
public static void main(String[] args) {
JFrame f = new JFrame("Test");
f.setSize(300, 300);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JTextArea textArea = new JTextArea(20, 40);
f.add(textArea);
f.pack();
f.setVisible(true);
}
}
Various operations for a JTextArea
• append a string
• set line wrapping
• get text
• get selected text
• set whether editable
• and so on
S. Bowers
5 of 10
Lecture Notes
CPSC 224 (Spring 2012)
Adding Scroll Bars to a Text Area
Here we can use a JScrollPane widget
import javax.swing.*;
public class Lab {
public static void main(String[] args) {
JFrame f = new JFrame("Test");
f.setSize(300, 300);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JTextArea textArea = new JTextArea(20, 40);
JScrollPane scrollPane = new JScrollPane(textArea);
f.add(scrollPane);
f.pack();
f.setVisible(true);
}
}
Setting the horizontal and vertical scroll policy
• as needed, never, always ... by scroll bar
scrollPane.setVerticalScrollBarPolicy(
ScrollPaneConstants.VERTICAL SCROLLBAR ALWAYS);
S. Bowers
6 of 10
Lecture Notes
CPSC 224 (Spring 2012)
Dialog Boxes
Displaying simple errors, warnings, messages, etc. using JOptionPane
JOptionPane.showMessageDialog(...)
– shows a message, waits for user to click OK
JOptionPane.showConfirmDialog(...)
– shows a message and gets confirmation (OK, cancel, etc.)
JOptionPane.showOptionDialog(...)
– shows a message and gets users choice from a set of options
JOptionPane.showInputDialog(...)
– shows a message and gets a line of user input
import javax.swing.*;
public class Lab {
public static void main(String[] args) {
JFrame f = new JFrame("Test");
f.setSize(300, 300);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
JOptionPane.showMessageDialog(f, "Welcome to Swing");
JOptionPane.showMessageDialog(f, "Hi", "Title",
JOptionPane.PLAIN_MESSAGE);
}
}
• Types of messages: ERROR MESSAGE, INFORMATION MESSAGE, WARNING MESSAGE, QUESTION MESSAGE, or PLAIN MESSAGE
S. Bowers
7 of 10
Lecture Notes
CPSC 224 (Spring 2012)
Basic Class Organization
Create JFrame or JPanel subclasses for windows/panes
• main creates the main application frame
• each JFrame or JPanel class becomes a reusable, specialized widget
public class App {
public static void main(String[] args) {
...
JFrame frame = new MyJFrame(...);
...
}
}
public class MyJFrame extends JFrame {
public MyJFrame(...) {
initFrame();
...
}
private void initFrame() { ... }
}
public class MyPane extends JPanel {
public MyPane() {
initPane();
}
private void initPane() { ... }
}
S. Bowers
8 of 10
Lecture Notes
CPSC 224 (Spring 2012)
Buttons
Create buttons using the JButton class
import javax.swing.*;
import java.awt.event.*;
public class Lab {
public static void main(String[] args) {
JFrame f = new JFrame("Test");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new PanicPane());
f.pack();
f.setVisible(true);
}
}
import javax.swing.*;
import java.awt.event.*;
public class PanicPane extends JPanel implements ActionListener {
private JButton button1 = new JButton("Panic");
private JButton button2 = new JButton("Don’t Panic");
public PanicPane() {
initPane();
}
private void initPane() {
button1.addActionListener(this);
button2.addActionListener(this);
add(button1);
S. Bowers
9 of 10
Lecture Notes
CPSC 224 (Spring 2012)
add(button2);
}
public void actionPerformed(ActionEvent e) {
if(e.getSource() == button1)
System.out.println("Panic");
else
System.out.println("Don’t Panic");
}
}
Exercise
• Instead of printing ...
• Display a dialog box with a message depending on button clicked
S. Bowers
10 of 10