CardLayout
is a special layout manager for creating the effect of a stack of
cards. Instead of arranging all of the container’s components,
it displays only one at a time. You might use this kind of layout to
implement a hypercard stack or a Windows-style set of configuration
screens. If CardLayout
sounds interesting, you
might also want to investigate the JTabbedPane
component, described in Chapter 14.
To add a component to a
CardLayout
, use a two-argument version of the
container’s add( )
method; the extra
argument is an arbitrary string that serves as the card’s name:
add("netconfigscreen", myComponent);
To bring a particular card to the top of the stack, call the
CardLayout
’s show( )
method
with two arguments: the parent Container
and the
name of the card you want to show. There are also methods like
first( )
, last( )
, next( )
, and previous( )
for working with the stack of cards. These are all
CardLayout
instance methods. To invoke them, you
need a reference to the CardLayout
object itself,
not to the container it manages. Each method takes a single argument:
the parent Container
. Here’s a simple
example:
//file: Card.java import java.awt.*; import java.awt.event.*; import javax.swing.*; public class Card extends JPanel { CardLayout cards = new CardLayout( ); public Card( ) { setLayout(cards); ActionListener listener = new ActionListener( ) { public void actionPerformed(ActionEvent e) { cards.next(Card.this); } }; JButton button; button = new JButton("one"); button.addActionListener(listener); add(button, "one"); button = new JButton("two"); button.addActionListener(listener); add(button, "two"); button = new JButton("three"); button.addActionListener(listener); add(button, "three"); } public static void main(String[] args) { JFrame f = new JFrame("Card"); f.addWindowListener(new WindowAdapter( ) { public void windowClosing(WindowEvent e) { System.exit(0); } }); f.setSize(200, 200); f.setLocation(200, 200); f.setContentPane(new Card( )); f.setVisible(true); } }
We add three buttons to the layout and cycle
through them as they are pressed. An anonymous inner class is used as
an action listener for each button; it simply calls
CardLayout
’s next( )
method whenever a button is pressed. In a more realistic example, we
would build a group of panels, each of which might implement some
part of a complex user interface, and add those panels to the layout.
Each panel would have its own layout manager. The panels would be
resized to fill the entire area available (i.e., the area of the
Container
they are in), and their individual
layout managers would arrange their internal components.