s.vanak@dcs.shef.ac.uk
File swing.tex – p. 1

• Java has two GUI (Graphics User Interface) packages, the original Abstract
Windows Toolkit or AWT and the newer Swing
• AWT used the native operating system’s window routines and therefore the visual effect was dependent on the run time system platform.
• Swing allows three modes: a unified ’Java’ look and feel [the default], the native platform look, or a specific platform’s look.
• Swing has quite a large overhead. Eclipse SWT tires to get the best of both worlds.
• We will be focusing on Swing and bit of AWT.
File swing.tex – p. 2

• Containers hold GUI controls or widgets. For example text fields check boxes etc.
• Other Widgets can be added to a Container using its add(Component) method.
• A Container is also a Component, this allows containers to be nested in order to create complex layouts.
• JPanel is one of the most commonly used containers.
• The is also the Box container for creating Row or Column wise layouts.
JPanel panel = new JPanel();
JTextField field1 = new JTextField(); panel.add(new JLabel("Field 1")); panel.add(field1); panel.add(new JButton("Ok"));
File swing.tex – p. 3

• As soon as you have more than one or two widgets (ie components or controls), you need to arrange them in a logical and pleasing way.
• A JPanel is a Container, which means that it can contain other components. GUI design in Java relies on a layered approach where each layer uses an appropriate layout manager.
• Layout managers are interface classes that align components so they neither crowd each other nor overlap.
• Each layout manager defines methods that arrange components within a container, and each component you place within a Container can also be a container itself.
• The Java platform supplies layout managers that range from the very simple
FlowLayout and GridLayout.
• to the special purpose BorderLayout and CardLayout, to the very flexible BoxLayout and GridBagLayout.
• SpringLayout is a new layout manager that uses the concepts of springs and struts to help design well-positioned containers.
File swing.tex – p. 4

• FlowLayout is used to arrange components in rows across the width of a container
• FlowLayout components automatically wrap or move to the next row when required.
• When you use FlowLayout, each component retains its default size (i.e. a JButton will be large enough to hold its text.
• A component might become partially obscured or change position or wrap due to the size of the container.
• You can fix a minimum size for the container by calling the
JComponent.setMinimumSize(int, int) method.
File swing.tex – p. 5

• uses a simple row and column grid metaphor for layout. All elements are of the same width and height and scale similarly when resized. The constructor is
GridLayout(rows,columns,x-spacing, y-spacing)
Places items in a single row or column. An example is:
JPanel panel = new JPanel();
BoxLayout box = new BoxLayout(panel,Boxlayout.Y_AXIS));
You may be better off using the Box class instead of BoxLayout.
• CardLayout presents widgets one at a time as if cards in a deck.
• A common use is a slideshow viewer where different panes are displayed one at a time.
File swing.tex – p. 6

• BorderLayout is used when you add components to a maximum of five sections arranged in North, South, East, West and Center positions.
• BorderLayout is the default manager for all content panes.
• When you place exactly five components in a container and use BorderLayout, each component fills one entire region.
• When the program runs, the Layout Manager determines the exact size of each component based on the component’s contents.
• North, South, East, West containers will take up their preferred sizes.
• the Center component will take up the rest of the space.
• Any empty component regions disappear from the layout.
JPanel p = new JPanel(new BorderLayout()); p.add(new JLabel("North"), BorderLayout.NORTH); p.add(new JLabel("South"), BorderLayout.SOUTH); p.add(new JLabel("East"), BorderLayout.EAST); p.add(new JLabel("West"), BorderLayout.WEST); p.add(new JLabel("Center"), BorderLayout.CENTER);
File swing.tex – p. 7

• Swings top level contains are: JFrame, JDialog, JWindow, JApplet.
• The most frequently used top level container is JFrame, and contains methods such as:
◦ setBounds(x,y,w,h)
◦ setLocation(x,y)
◦ setSize(w,h)
◦ setResizable(bool)
◦ setTitle(str)
◦ setVisible(bool)
◦ isResizable()
◦ getTitle()
◦ getContentPane()
File swing.tex – p. 8

All GUI processing must occur within the Event Dispatch Thread.
The following code creates a frame in the “main” thread.
public static void main(String[] args) {
JFrame app = new JFrame(); app.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); app.setVisible(true);
}
Creating a frame in the EDT public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() { public void run() {
JFrame app = new JFrame(); app.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); app.setVisible(true);
}
});
}
File swing.tex – p. 9

• A JFrame is made up of many components.
• When adding components to a JFrame you must add the compoents to the Content
Pane of the JFrame.
• In Java 1.4.x you must do frame.getContentPane().add(Component)
• In Java 1.5 has make JFrame.add(Component) the same as frame.getContentPane().add(Component)
File swing.tex – p. 10

• GUIs are event-based. That is they respond to buttons, keyboard input or mouse activities.
• Java uses event listeners to monitor activity on specified objects and react to specific conditions.
• The most common Listener interface for GUI component is ActionListener.
• An ActionEvent is generated when ever a component receives a user actions. e.g.
clicking a JButton, pressing enter on a JTextField.
• Other listener interfaces include, Focus Listener, MouseListener,
ListSelectionListener.
• For listener interfaces that contain more than one method, the API also has Adaptor classes for the interface.
• The Adaptor is simply a class that implements the Listener as empty methods.
File swing.tex – p. 11

• There are two methods: Have the class implement the listener, or create a new class.
class MyPanel extends JPanel implements ActionListener {
JButton b = new JButton("Ok");
MyPanel() { super(); b.addActionListener(this);
}
} public void actionPerformed(ActionEvent e) { if (e.getSource() == b) {
// Do something
}
}
File swing.tex – p. 12

File swing.tex – p. 13

File swing.tex – p. 14

• Simple dialogs appear in popup windows.
• Dialogs include:
◦ Short messages or information screens
◦ confirmation boxes.
◦ input prompts for string information.
• Swing uses the JOptionPane class to provide methods for each type of dialog.
• Each method has a first parameter that points to a parent (ie. window that it appears in) or null (default to the current window).
• Dialog boxes will block until the user returns an input. Removing the need to listen for an event.
File swing.tex – p. 15

JOptionPane.showMessageDialog(null,"This is just a message",
"Message Dialog",JOptionPane.PLAIN_MESSAGE); int pressed = JOptionPane.showConfirmBox(null,"Everything aok"); if (pressed == JOptionPane.YES_OPTION) {
// do the action for confirmation
}
String user_data = JOptionPane.showInputDialog(null,"What’s your name");
File swing.tex – p. 16