Java Reference
In-Depth Information
Putting borders around JComponents . This is an advanced topic. There is a way to put a bor-
der around any JComponent , like a JButton or a JPanel . You cannot put a bor-
der around a Box this way, but you get that effect by adding the Box as the only
component of a JPanel and then putting a border around the JPanel .
A footnote at the bottom of lesson page 17-3 of the CD shows you how to
put borders around JComponents and gives several examples.
Containers and layout managers
Class JFrame is a subclass of class Container , which means that it can contain
components like buttons and labels. JFrame , with a BorderLayout manager,
may seem rather limited because it can contain only five components —in the
east, north, west, south, and center.
We introduce two other containers, the Jpanel and the Box , which have lay-
out managers FlowLayout and BoxLayout , respectively. Instances of JPanel
and Box can be added as components to a JFrame —or even to another JPanel
or Box . This nesting of containers allows us to construct a JFrame whose layout
is quite complex and that can contain any number of components.
There are other layout managers, e.g. CardLayout , GridBagLayout ,
GridLayout , and OverlayLayout . We do not discuss them.
import java.awt.*;
import javax.swing.*;
/** An instance has labels in the north and south and a JPanel with four buttons in the center */
public class PanelDemo extends JFrame {
JPanel p= new JPanel();
/** Constructor: an invisible frame with title t , 2 labels, and a 4-button JPanel */
public PanelDemo(String t) {
super (t);
p.add( new JButton("0"));
p.add( new JButton("1"));
p.add( new JButton("2"));
p.add( new JButton("3"));
Container cp= getContentPane();
cp.add( new JLabel("north"),BorderLayout.NORTH);
cp.add( new JLabel("south"),BorderLayout.SOUTH);
Figure 17.10:
Class PanelDemo
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