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Chapter 14
More Swing Objects
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Chapter 14
Menus
Making GUIs Pretty (and More Functional)
Box Containers and Box Layout Managers
More on Events and Listeners
Another Look at the Swing Class Hierarchy
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Menus
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Three Swing classes used to put a menu in a
program:
AbstractButton
» JMenuBar
» JMenu
JMenuItem
» JMenuItem
JButton
JMenu
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Chapter 14
Menu items behave in the same way as buttons
Java: an Introduction to Computer Science & Programming - Walter Savitch
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A GUI with
a Menu
JMenu memoMenu = new JMenu("Memos");
JMenuItem m;
Create a menu
m = new JMenuItem("Save Memo 1");
m.addActionListener(this);
memoMenu.add(m);
Create a menu item
m = new JMenuItem("Save Memo 2");
m.addActionListener(this);
A menu item uses an
memoMenu.add(m);
action listener the same
. . .
JMenuBar mBar = new JMenuBar(); way a button does.
mBar.add(memoMenu);
setJMenuBar(mBar);
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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A GUI with
a Menu
JMenu memoMenu = new JMenu("Memos");
JMenuItem m;
m = new JMenuItem("Save Memo 1");
Each menu item is added
m.addActionListener(this);
to the menu.
memoMenu.add(m);
m = new JMenuItem("Save Memo 2");
m.addActionListener(this);
The menu is added to the
memoMenu.add(m);
menu bar.
. . .
JMenuBar mBar = new JMenuBar();
mBar.add(memoMenu);
setJMenuBar(mBar);
One way to add a menu
bar to a JFrame
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Nested Menus
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JMenu is a descendant of JMenuItem
Every JMenu object is also a JMenuItem
A JMenu can be a menu item in another menu
This allows nested menus
Clicking on a nested menu shows the items in the
nested menu and allows them to be selected.
AbstractButton
JMenuItem
JButton
JMenu
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Making GUIs Pretty
(and More Functional)
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Chapter 14
Adding Icons
The JScrollPane Class for Scroll Bars
Adding Borders
Changing the Look and Feel
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Using Icons
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Icons are (small) pictures
Icons may be added to labels, buttons, and menu items.
The ImageIcon class can be used to convert a picture to an icon:
ImageIcon SmileyFaceIcon = new ImageIcon(“smiley.gif”);
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The setIcon method can be used to add an icon to a component:
JLabel helloLabel = new JLabel(“Hello”);
ImageIcon dukeWavingIcon =
new ImageIcon(“duke_waving.gif”);
helloLabel.setIcon(dukeWavingIcon);
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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The JScrollPane Class for Scroll Bars
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A view port is used when not all information can be displayed on
screen at once.
Scroll bars move a view port around to show different parts of the
information.
JScrollPane is a class that can provide a view port with scroll bars.
An example using JScrollPane with a JTextArea called theText
and a JPanel called textPanel:
JScrollPane scrolledText = new JScrollPane(theText);
textPanel.add(scrolledText);
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Adding Borders
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A border is an area that frames a component.
Swing provides several different types of borders:
» BevelBorder—makes component look raised or lowered
» EtchedBorder—similar to BevelBorder but can’t set size
» EmptyBorder—extra space around the component
» LineBorder—colored border of a given thickness
» MatteBorder—similar to LineBorder but can adjust
thickness on each side of the component
An example of adding a bevel border to a button:
testButton.setBorder(new BevelBorder(BevelBorder.LOWERED));
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Changing the Look and Feel
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Chapter 14
Look and feel refers to the general appearance of the GUI,
including:
» Shape and exact placement of buttons
» Default colors
Three standard choices for look and feel:
» Metal—considered the standard Java look and feel
» Motif—often considered the standard Unix look and feel
» Windows—looks like the windows you get with the Windows
operating system
A Macintosh look and feel is also available
Java: an Introduction to Computer Science & Programming - Walter Savitch
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An Example of Changing the Look
and Feel of a GUI
try
Fully qualified class name—
{
includes directory path
UIManager.setLookAndFeel(
“com.sun.java.swing.plaf.motif.MotifLookAndFeel”);
SwingUtilities.updateComponentTreeUI(this);
}
Try and catch necessary
catch (Exception e)
because any one of four
{
exceptions could be thrown
System.out.println(
“Could not load the Motif look and feel”);
}
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Box Layout Manager
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Chapter 14
Useful for a single column or single row of
components
Specify X_AXIS (horizontal) or Y_AXIS (vertical)
layout as second parameter to constructor for layout
manager
Provides a means of separating components in a row
or column
» Strut—allocates a fixed amount of space between
two components
» Glue—allocates a variable amount of space
between two components
A Box container is a container that is automatically
given a BoxLayout manager.
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Box Layout Versus Other Layouts
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Chapter 14
Horizontal box layout is similar to flow layout.
Vertical box layout is similar to grid layout with only
one column.
Big advantage of box layout is control over spacing
using struts and glue.
Note that struts and glue should not be used with
other layout managers.
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Box Layout Demo Program
Specifies a
horizontal layout
JPanel horizontalPanel = new JPanel();
horizontalPanel.setLayout(
new BoxLayout(horizontalPanel, BoxLayout.X_AXIS));
Component horizontalStrut =
Box.createHorizontalStrut(HORIZONTAL_STRUT_SIZE);
horizontalPanel.add(horizontalStrut);
JButton hStopButton = new JButton("Red");
hStopButton.addActionListener(this);
horizontalPanel.add(hStopButton);
Static method in Box class used to create
a strut of a particular size for spacing
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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The WindowListener Interface
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Chapter 14
For a class to be a listener for window events, it must
implement the WindowListener interface.
By implementing the WindowListener interface, a
window can be its own listener.
The advantage of making a window its own listener is
that it is easy to call methods from the listener since
they are in the same object.
Java: an Introduction to Computer Science & Programming - Walter Savitch
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The WindowListener Interface
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Implementation of the WindowListener interface requires
these seven methods to be defined:
» public void windowOpened(WindowEvent e)
» public void windowClosing(WindowEvent e)
» public void windowClosed(WindowEvent e)
» public void windowIconified(WindowEvent e)
» public void windowDeiconified(WindowEvent e)
» public void windowActivated(WindowEvent e)
» public void windowDeactivated(WindowEvent e)
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If a method will be not be used, it should be defined with an
empty body
WindowAdapter is a class that implements all seven methods
of the WindowListener with empty bodies.
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Java: an Introduction to Computer Science & Programming - Walter Savitch
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Programming the Close-Window
Button
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The WindowListener interface can be used to program the
close-window button.
If the close-window button is not programmed, by default it will
close the window but not exit the program.
For a window that does not close when the close-window button
is clicked, use a method call like this:
setDefaultCloseOperation(
WindowConstants.DO_NOTHING_ON_CLOSE);
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Chapter 14
The CloseWindowDemo uses this method call
When the close-window button is clicked, the program displays
a confirmation dialog instead of closing the window.
Java: an Introduction to Computer Science & Programming - Walter Savitch
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CloseWindowDemo Program
Prevents window from closing so
public CloseWindowDemo()
that user can confirm or cancel
{
before window is closed.
setSize(WIDTH, HEIGHT);
setDefaultCloseOperation(
WindowConstants.DO_NOTHING_ON_CLOSE);
addWindowListener(new InnerDestroyer());
setTitle("Close Window Demo");
Defined
Container contentPane = getContentPane();
on next
contentPane.setLayout(new BorderLayout()); slide
. . .
}
Constructor for the CloseWindowDemo
class, which inherits from JFrame.
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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CloseWindowDemo Program
Definition of inner class
used as listener for the
CloseWindowDemo class.
Inherits from WindowAdapter so
it does not have to define all seven
window event methods.
private class InnerDestroyer extends WindowAdapter
{
public void windowClosing(WindowEvent e)
{
ConfirmWindow askWindow = new ConfirmWindow();
askWindow.setVisible(true);
}
ConfirmWindow closes window and
}
exits program if user confirms close.
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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CloseWindowDemo Program
actionPerformed method from the
ConfirmWindow inner class
The main window
will only be
closed if the user
clicks the “Yes”
button in the
ConfirmWindow
public void actionPerformed(ActionEvent e)
{
if (e.getActionCommand().equals("Yes"))
System.exit(0);
else if (e.getActionCommand().equals("No"))
dispose(); //Destroys only the ConfirmWindow.
else
System.out.println("Error in Confirm Window.");
}
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Changing Components
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Chapter 14
A program can add or remove components after a
GUI has been displayed, but that is beyond the scope
of the book.
Making components visible or not visible gives a
similar effect.
The setVisible method is used in the
VisibleDemo program to make only one of the red
and green labels visible at a time.
(code on next slide)
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Changing Components
The actionPerformed method from the VisibleDemo program
public void actionPerformed(ActionEvent e)
{
if (e.getActionCommand().equals(“Red”))
{
colorPanel.setBackground(Color.red);
stopLabel.setVisible(false);
goLabel.setVisible(true); There is similar code for
validate();
when the Green button is
Visibility changes won’t
pressed, which turns the
}
occur until the validate
background green and
. . .
method is called.
hides the go label.
}
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Another Look at the Swing Class Hierarchy
JComponent
Swing
AbstractButton
JLabel
JMenuBar
JMenuItem
Abstract Class
Class
JButton
JMenu
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All of the basic properties of JButton and JMenuItem are inherited
from AbstractButton.
JButton and JMenuItem are similar because they are derived from
the same abstract class.
Since AbstractButton is an abstract class, no objects of that class
can be made.
The purpose of the AbstractButton class is to provide a place for
code that is common to JButton and JMenuItem and avoid repeated
code.
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Another Look at the Swing Class Hierarchy
JComponent
Swing
AbstractButton
JLabel
JMenuBar
JMenuItem
Abstract Class
Class
JButton
JMenu
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JLabel and JButton inherit from a common ancestor, namely
Jcomponent, so they have some similarities.
Notice, however, that JLabel and JButton are not derived from the
same class, even though they have a common ancestor.
The hierarchy reflects the fact that JButton and JMenuItem are more
similar than JLabel and JButton.
Also notice that JMenu inherits from JMenuItem, so it can be used
anywhere a JMenuItem can. This allows nested menus.
Chapter 14
Java: an Introduction to Computer Science & Programming - Walter Savitch
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Summary
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Chapter 14
You can add icons to JButtons, JLabels, and JMenuItems.
A JMenuBar can be added to a JFrame with the method
setJMenuBar or with the usual add method.
Both buttons and menu items fire action events and so should have
an ActionListener registered with them.
You can use the class JScrollPane to add scroll bars to a text area.
You can define a window listener class by having it implement the
WindowListener interface.
When you define a GUI using Swing you can specify the look and feel
for the GUI.
If you want a close-button to do something other than close the
window, you must use SetDefaultCloseOperation.
If you change the visibility of a component you should use the
validate method to update the GUI.
Java: an Introduction to Computer Science & Programming - Walter Savitch
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