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Exploring Java

Previous Chapter 12
Layout Managers

12.4 CardLayout

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 would use this kind of layout to implement a hypercard stack or a Windows-style set of configuration screens. When you add a component to the layout, you use the two-argument version of add(); 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 methods take a single argument: the parent Container. Here's a simple example:

import java.awt.*; 
public class main extends java.applet.Applet { 
    CardLayout cards = new CardLayout(); 
    public void init() { 
        setLayout( cards ); 
        add( new Button("one"), "one" ); 
        add( new Button("two"), "two" ); 
        add( new Button("three"), "three" ); 
    public boolean action( Event e, Object arg) { 
        cards.next( this ); 
        return true; 

We add three buttons to the layout and cycle through them as they are 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.

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