componenteventdemo.java

Java实现复选框

/*
 * ComponentEventDemo.java is a 1.4 example that requires
 * no other files.
 */

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

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();
            }
        });
    }
}