1
Chapter 4
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
More Swing Objects
2
Menus Three Swing classes used to put a menu in
a program:»JMenuBar»JMenu»JMenuItem
Menu items behave in the same way as buttons
AbstractButton
JButton
JMenu
JMenuItem
3
A GUI witha Menu
JMenu memoMenu = new JMenu("Memos");JMenuItem m; m = new JMenuItem("Save Memo 1"); m.addActionListener(this);memoMenu.add(m); m = new JMenuItem("Save Memo 2"); m.addActionListener(this);memoMenu.add(m);. . .JMenuBar mBar = new JMenuBar();mBar.add(memoMenu);setJMenuBar(mBar);
Create a menu
Create a menu item
A menu item uses an action listener the same way a button does.
4
A GUI witha Menu
JMenu memoMenu = new JMenu("Memos");JMenuItem m; m = new JMenuItem("Save Memo 1"); m.addActionListener(this);memoMenu.add(m); m = new JMenuItem("Save Memo 2"); m.addActionListener(this);memoMenu.add(m);. . .JMenuBar mBar = new JMenuBar();mBar.add(memoMenu);setJMenuBar(mBar);
Each menu item is added to the menu.
The menu is added to the menu bar.
One way to add a menu bar to a JFrame
5
Nested Menus 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
JButton
JMenu
JMenuItem
6
Making GUIs Pretty(and More Functional)
Adding Icons The JScrollPane Class for Scroll Bars Adding Borders Changing the Look and Feel
7
Using Icons
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”);
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);
8
The JScrollPane Class for Scroll Bars
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);
9
Adding Borders 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));
10
11
12
13
Changing the Look and Feel 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
14
An Example of Changing the Look and Feel of a GUI
try{ UIManager.setLookAndFeel( “com.sun.java.swing.plaf.motif.MotifLookAndFeel”);
SwingUtilities.updateComponentTreeUI(this);}catch (Exception e){ System.out.println( “Could not load the Motif look and feel”);}
Fully qualified class name— includes directory path
Try and catch necessary because any one of four exceptions could be thrown
15
Box Layout Manager 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.
16
Box Layout Versus Other Layouts
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.
17
Box Layout Demo Program
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
Specifies a horizontal layout
18
The WindowListener Interface 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.
19
The WindowListener Interface 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)
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.
20
Programming the Close-Window Button
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);
The CloseWindowDemo uses this method call When the close-window button is clicked, the program
displays a confirmation dialog instead of closing the window.
21
CloseWindowDemo Program
public CloseWindowDemo()
{
setSize(WIDTH, HEIGHT);
setDefaultCloseOperation(
WindowConstants.DO_NOTHING_ON_CLOSE);
addWindowListener(new InnerDestroyer());
setTitle("Close Window Demo");
Container contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
. . .
}
Prevents window from closing so that user can confirm or cancel before window is closed.
Constructor for the CloseWindowDemo class, which inherits from JFrame.
Defined on next slide
22
CloseWindowDemo Program
private class InnerDestroyer extends WindowAdapter{ public void windowClosing(WindowEvent e) { ConfirmWindow askWindow = new ConfirmWindow(); askWindow.setVisible(true); }}
Inherits from WindowAdapter so it does not have to define all seven window event methods.
Definition of inner class used as listener for the CloseWindowDemo class.
ConfirmWindow closes window and exits program if user confirms close.
23
CloseWindowDemo Program
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.");
}
actionPerformed method from the ConfirmWindow inner class
The main window will only be closed if the user clicks the “Yes” button in the ConfirmWindow
24
Changing Components 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)
25
Changing Components
public void actionPerformed(ActionEvent e)
{
if (e.getActionCommand().equals(“Red”))
{
colorPanel.setBackground(Color.red);
stopLabel.setVisible(false);
goLabel.setVisible(true);
validate();
}
. . .
}
There is similar code for when the Green button is pressed, which turns the background green and hides the go label.
The actionPerformed method from the VisibleDemo program
Visibility changes won’t occur until the validate method is called.
26
JComponent
JLabel JMenuBar
AbstractButton
JButton
JMenu
JMenuItem
Swing
Class
Abstract Class
Another Look at the Swing Class Hierarchy
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.
27
JComponent
JLabel JMenuBar
AbstractButton
JButton
JMenu
JMenuItem
Swing
Class
Abstract Class
Another Look at the Swing Class Hierarchy
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.
28
Summary 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.