Application Development using Traditional Programming

Traditional Programming means writing codes and calling API directly. It offers the highest degree of flexibility for custom application development.

Tutorial #1: Network Communication
Tutorial #2: Device Driver
Tutorial #3: Intelligent Agent

Tutorial #1: Network Communication This tutorial describes how to use the World Wide Lab ^TM communication package, weblab.net. Example codes are in test_net directory. In general, the process involves:

Make sure WhiteBoard process is running on the communication server machine.
Write the code for Publisher process using the Publisher class.
Write the code for Subscriber process using the Subscriber class.

Write the code for Publisher process

To implement a process that performs the Publisher role, we need to :

Create a Publisher object, give it a unique name, and tell it where is the WhiteBoard. Fo example: publisher = new Publisher(name, WhiteBoardConf.SERVER_NAME);
Define an unique Suject name to publish. For example: publisher.addSubject("warning");
Publish the data under a Subject name. For example: publisher.setValue("warning", "my message");

The following is the source code for PUser.java which uses a TextArea to collect input.
When the "submit" botton is pressed, it publishes the data to WhiteBoard.

import java.io.*;
import java.awt.*;
import java.awt.event.*;

import weblab.net.*;

public class PUser
extends Frame
implements MouseListener
{
TextArea text; // content of text window
Button submit_button;
Publisher publisher;

// **********************************************************
// Constructor
// **********************************************************
public PUser(String name)
{
super(name);

    // establish a publisher for data
    publisher = new Publisher(name, WhiteBoardConf.SERVER_NAME);
    publisher.addSubject("warning");

    // set up GUI objects
    setLayout(new BorderLayout());
    add("Center", text = new TextArea());
    add("South", submit_button = new Button("Publish"));
    submit_button.addMouseListener(this); // this object listens to mouse
    setSize(300,300);
    show();
}

// **********************************************************
// MouseListener Interface implementation
// **********************************************************
public void mouseClicked(MouseEvent me) {
publisher.setValue("warning", text.getText());
}

public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public void mousePressed(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}

//
// launch this object
//
public static void main(String args[]) {
new PUser("PublisherUser");
}

}

Write the code for Subscriber process

To implement a process that performs the Subscriber role, we need to :

Create a Subscriber object, give it a unique name such a host name, and tell it where is the

WhiteBoard. For example: subscriber = new Subscriber(local_host.getHostName(), WhiteBoardConf.SERVER_NAME, this);
Define a Suject name to subscribe. For example: subscriber.subscribe(SUBJECT);
Implement the SubscriberUser Interface, update(), to handle Subject update callback. For example:

public void update(String name, Object s) {

text.setText((String)s);

}

The following is the source code for SUser.java which uses a TextArea to display the latest
message on the Subject from its Publisher.

import java.io.*;
import java.awt.*;
import java.awt.event.*;
import java.net.InetAddress;

import weblab.net.*;

public class SUser
extends Frame
implements SubscriberUser
{
Subscriber subscriber;
TextArea text; // content of text window
InetAddress local_host; // local host network address
String SUBJECT= "warning"; // subject name to subscribe

// **********************************************************
// CONSTRUCTOR
// **********************************************************
public SUser(String name) {
super(name);

    // get local host address
    try {
      local_host = InetAddress.getLocalHost();// use class static method to get a ref
    }
    catch (Exception e) {
      System.out.println("can't find local network address.");
      System.exit(1);
    }

    // establish a subscriber helper object
    subscriber = new Subscriber(local_host.getHostName(),
                                WhiteBoardConf.SERVER_NAME,
                                this);
    Object value = subscriber.subscribe(SUBJECT);

    // set up GUI objects
    setLayout(new BorderLayout());
    add("Center", text = new TextArea());

    // get latest value ASAP
    if (value != null)
      update(SUBJECT, value);

setSize(300,300);
show();
}

// **********************************************************
// SubscriberUser Interface implementation
// **********************************************************
public void update(String name, Object s) {
text.setText((String)s);
}

//
// launch this object
//
public static void main(String args[]) {
new SUser("SubscriberUser");
}

}

Tutorial #2: Device Driver under construction

Tutorial #3: Intelligent Agent under construction

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