/* * Swing version */import javax.swing.*;import java.awt.Dimension;import java.awt.GridBagLayout;import java.awt.GridBagConstraints;import java.awt.event.ContainerEvent;import java.awt.event.ContainerListener;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.util.Vector;public class ContainerEventDemo extends JApplet                                 implements ContainerListener,                                           ActionListener {    JTextArea display;    JPanel buttonPanel;    JButton addButton, removeButton, clearButton;    Vector buttonList;    static final String ADD = "add";    static final String REMOVE = "remove";    static final String CLEAR = "clear";    static final String newline = "\n";    public void init() {        //Initialize an empty list of buttons.        buttonList = new Vector(10, 10);        //Create all the components.        addButton = new JButton("Add a button");        addButton.setActionCommand(ADD);        addButton.addActionListener(this);        removeButton = new JButton("Remove a button");        removeButton.setActionCommand(REMOVE);        removeButton.addActionListener(this);        buttonPanel = new JPanel();        buttonPanel.setPreferredSize(new Dimension(200, 75));        buttonPanel.addContainerListener(this);        display = new JTextArea();        display.setEditable(false);        JScrollPane scrollPane = new JScrollPane(display);        scrollPane.setPreferredSize(new Dimension(200, 75));        clearButton = new JButton("Clear text area");        clearButton.setActionCommand(CLEAR);        clearButton.addActionListener(this);        //Lay out the components.        GridBagLayout gridbag = new GridBagLayout();        GridBagConstraints c = new GridBagConstraints();        JPanel contentPane = new JPanel();        contentPane.setLayout(gridbag);        c.fill = GridBagConstraints.BOTH; //Fill entire cell.        c.weighty = 1.0;  //Button area and message area have equal height.        c.gridwidth = GridBagConstraints.REMAINDER; //end of row        gridbag.setConstraints(scrollPane, c);        contentPane.add(scrollPane);        c.weighty = 0.0;          gridbag.setConstraints(clearButton, c);        contentPane.add(clearButton);        c.weightx = 1.0;  //Add/remove buttons have equal width.        c.gridwidth = 1;  //NOT end of row        gridbag.setConstraints(addButton, c);        contentPane.add(addButton);        c.gridwidth = GridBagConstraints.REMAINDER; //end of row        gridbag.setConstraints(removeButton, c);        contentPane.add(removeButton);        c.weighty = 1.0;  //Button area and message area have equal height.        gridbag.setConstraints(buttonPanel, c);        contentPane.add(buttonPanel);        setContentPane(contentPane);    }    public void componentAdded(ContainerEvent e) {        displayMessage(" added to ", e);    }    public void componentRemoved(ContainerEvent e) {        displayMessage(" removed from ", e);    }    void displayMessage(String action, ContainerEvent e) {        display.append(((JButton)e.getChild()).getText()                       + " was"                       + action                       + e.getContainer().getClass().getName()                       + newline);    }    /*     * This could have been implemented as two or three     * classes or objects, for clarity.     */    public void actionPerformed(ActionEvent e) {        String command = e.getActionCommand();        if (command == ADD) {            JButton newButton = new JButton("JButton #"                                          + (buttonList.size() + 1));            buttonList.addElement(newButton);            buttonPanel.add(newButton);            buttonPanel.revalidate(); //Make the button show up.        } else if (command == REMOVE) {            int lastIndex = buttonList.size() - 1;            try {                JButton nixedButton = (JButton)buttonList.elementAt(lastIndex);                buttonPanel.remove(nixedButton);                buttonList.removeElementAt(lastIndex);                buttonPanel.revalidate(); //Make the button disappear.                buttonPanel.repaint(); //Make the button disappear.            } catch (ArrayIndexOutOfBoundsException exc) {}        } else if (command == CLEAR) {            display.setText("");        }    }}