Graphical User Interfaces - Java - page 548

populate the frame. But some less-educated folk, and those in a hurry, often added compon-
ents directly to the frame. The Swing JFrame is more complex—it comes with not one but
two containers already constructed inside it. The ContentPane is the main container; you
should normally use it as your JFrame 's main container. The GlassPane has a clear back-
ground and sits over the top of the ContentPane ; its primary use is in temporarily painting
something over the top of the main ContentPane . Because of this, you need to use the
JFrame 's getContentPane() method:

public public class class ContentPane ContentPane extends extends JFrame {

public public ContentPane () {

Container cp = getContentPane ();
// now add Components to "cp"...
cp . add ( new

new JLabel ( "A Really Simple Demo" , JLabel . CENTER ));

}

}

You can add any number of components (including containers) into this existing container,
using the ContentPane add() method:

public public class class JFrameDemo JFrameDemo extends extends JFrame {

private private static static final final long long serialVersionUID = - 3089466980388235513L ;

JButton quitButton ;

/** Construct the object including its GUI */
public public JFrameDemo () {

super

super ( "JFrameDemo" );
Container cp = getContentPane ();
cp . setLayout ( new new FlowLayout ());

cp . add ( quitButton = new

new JButton ( "Exit" ));

// Set up so that "Close" will exit the program,
// not just close the JFrame.
setDefaultCloseOperation ( JFrame . EXIT_ON_CLOSE );

// This "action handler" will be explained later in the chapter.
quitButton . addActionListener ( new new ActionListener () {

public public void void actionPerformed ( ActionEvent e ) {

setVisible ( false

false );

dispose ();
System . exit ( 0 );