Component Event Demo
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/*
* ComponentEventDemo.java is a 1.4 example that requires no other files.
*/
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JCheckBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
public class ComponentEventDemo extends JPanel implements ComponentListener,
ItemListener {
static JFrame frame;
JTextArea display;
JLabel label;
String newline = "\n";
public ComponentEventDemo() {
super(new BorderLayout());
display = new JTextArea();
display.setEditable(false);
JScrollPane scrollPane = new JScrollPane(display);
scrollPane.setPreferredSize(new Dimension(350, 200));
JPanel panel = new JPanel(new BorderLayout());
label = new JLabel("This is a label", JLabel.CENTER);
label.addComponentListener(this);
panel.add(label, BorderLayout.CENTER);
JCheckBox checkbox = new JCheckBox("Label visible", true);
checkbox.addItemListener(this);
checkbox.addComponentListener(this);
panel.add(checkbox, BorderLayout.PAGE_END);
panel.addComponentListener(this);
add(scrollPane, BorderLayout.CENTER);
add(panel, BorderLayout.PAGE_END);
frame.addComponentListener(this);
}
public void itemStateChanged(ItemEvent e) {
if (e.getStateChange() == ItemEvent.SELECTED) {
label.setVisible(true);
//Need to revalidate and repaint, or else the label
//will probably be drawn in the wrong place.
label.revalidate();
label.repaint();
} else {
label.setVisible(false);
}
}
protected void displayMessage(String message) {
//If the text area is not yet realized, and
//we tell it to draw text, it could cause
//a text/AWT tree deadlock. Our solution is
//to ensure that the text area is realized
//before attempting to draw text.
if (display.isShowing()) {
display.append(message + newline);
display.setCaretPosition(display.getDocument().getLength());
}
}
public void componentHidden(ComponentEvent e) {
displayMessage("componentHidden event from "
+ e.getComponent().getClass().getName());
}
public void componentMoved(ComponentEvent e) {
Component c = e.getComponent();
displayMessage("componentMoved event from " + c.getClass().getName()
+ "; new location: " + c.getLocation().x + ", "
+ c.getLocation().y);
}
public void componentResized(ComponentEvent e) {
Component c = e.getComponent();
displayMessage("componentResized event from " + c.getClass().getName()
+ "; new size: " + c.getSize().width + ", "
+ c.getSize().height);
}
public void componentShown(ComponentEvent e) {
displayMessage("componentShown event from "
+ e.getComponent().getClass().getName());
}
/**
* Create the GUI and show it. For thread safety, this method should be
* invoked from the event-dispatching thread.
*/
private static void createAndShowGUI() {
//Make sure we have nice window decorations.
JFrame.setDefaultLookAndFeelDecorated(true);
//Create and set up the window.
frame = new JFrame("ComponentEventDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new ComponentEventDemo();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
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