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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

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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

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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.

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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

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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

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Making GUIs Pretty(and More Functional)

Adding Icons The JScrollPane Class for Scroll Bars Adding Borders Changing the Look and Feel

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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);

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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);

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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));

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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

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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

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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.

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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.

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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

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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.

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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.

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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.

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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

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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.

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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

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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)

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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.

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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.

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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.

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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.