ComponentListener event handling

ComponentListener with Text field and Frame example. event handling
java code

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class ComponentEventExample extends Applet
			        implements ComponentListener,
			                   ActionListener {
    TextArea textAreaObj;
    Frame frameObj;
    public boolean showIt = false;
    final static String showMessage = "show";
    final static String emptyMessage = "empty";
    String newline;

    public void init() {
	lineSeparator = System.getProperty("line.separator");
	setLayout(new BorderLayout());

	textAreaObj = new TextArea(5, 25);
	textAreaObj.setEditable(false);
	add("Center", textAreaObj);

	Button btnObj1 = new Button("Start");
	btnObj1.setActionCommand(showMessage);
	btnObj1.addActionListener(this);
	add("North", btnObj1);

	Button btnObj2 = new Button("Clear");
	btnObj2.setActionCommand(emptyMessage);
	btnObj2.addActionListener(this);
	add("South", btnObj2);

	frameObj = new Frame("My Frame");
	comPanel comPanelObj = new comPanel(this);
	frameObj.addComponentListener(this);
	comPanelObj.addComponentListener(this);
	frameObj.add("Center", comPanelObj);
	frameObj.pack();

	frameObj.addWindowListener(new WindowAdapter() {
	    public void windowClosing(WindowEvent e) {
		showIt = false;
		frameObj.setVisible(false);
	    }
	});
    }
    //
    public void actionPerformed(ActionEvent e) {
	 // condition to do action
	 // print the content of getActionCommand() if you want.
	if (e.getActionCommand() == showMessage) {
	    showIt = true;
	    frameObj.setVisible(true);
	} else { // clear textArea content.
	    textAreaObj.setText("");
	}
    }

    public void stop() {
	frameObj.setVisible(false);
    }

    public void start() {
	if (showIt) {
	    frameObj.setVisible(true);
	}
    }

    protected void displayMessage(String message) {
	try {
	    textAreaObj.append(message + lineSeparator);
	} catch (Exception event) {}
    }

    public void componentHidden(ComponentEvent e) {
	displayMessage("componentHidden event from "
		       + e.getComponent().getClass().getName());
    }

    public void componentMoved(ComponentEvent e) {
	displayMessage("componentMoved event from "
		       + e.getComponent().getClass().getName());
    }

    public void componentResized(ComponentEvent e) {
	displayMessage("componentResized event from "
		       + e.getComponent().getClass().getName());
    }

    public void componentShown(ComponentEvent e) {
	displayMessage("componentShown event from "
		       + e.getComponent().getClass().getName());
    }
}

class comPanel extends Panel 
		     implements ItemListener {
    Label labelObj;
    Checkbox checkBoxObj;

    comPanel(ComponentEventExample listener) {
	setLayout(new BorderLayout());

	labelObj = new Label("Label", Label.CENTER);
	add("Center", labelObj);

	checkBoxObj = new Checkbox("Label visible", true);
	checkBoxObj.addItemListener(this);
	add("South", checkBoxObj);

	labelObj.addComponentListener(listener);
	checkBoxObj.addComponentListener(listener);
    }

    public void itemStateChanged(ItemEvent e) {
	if (e.getStateChange() == ItemEvent.SELECTED) {
	    labelObj.setVisible(true);
	} else {
	    labelObj.setVisible(false);
	}
    }
}