DCO10101 Introduction to Information System

Event and ActionListener

Events occur when users interact with your program
<INPUT TYPE="button" VALUE="press me">

Occurence of Events must be communicated among a set of processes and handled

the <INPUT> element and the JavaScript function UpdateCells()

<SCRIPT LANGUAGE="JavaScript">
<!--
function UpdateCells() {
  top.location = "http://www.cityu.edu.hk/";
}
// -->
</SCRIPT>

In JAVA, events are handled using the delegation event model e.g. A button when pressed generated an ActionEvent object. ActionListener is an interface that contains a single method actionPerformed(ActionEvent e) which is automatically invoked when a button is pressed.

//filename: CityButton.java
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.net.*;
public class CityButton extends Applet implements ActionListener
{	
  public Button bCityU;
  public void init( )
  {
    bCityU = new Button("CityU");
    add(bCityU);
    bCityU.addActionListener(this);
  }

  public void actionPerformed(ActionEvent e)
  {
   try {
    URL url = new URL("http://www.cityu.edu.hk");
    if (e.getActionCommand().equals("CityU"))
	getAppletContext().showDocument(url);
	 } catch(MalformedURLException mue) {}
  }
}

Previou page