1.4. Java Programming

DataHub APIs for C++, Java, and .NET : Version 6.4
	Chapter 1. Introduction

The Java API implements the DataHubConnector class as the basic class used to communicate with the Cascade DataHub. Programmers writing stand-alone applications need only the DataHubConnector and DataHubPoint classes.

Java Class Overview

The following classes are included in the Java API installation. They are informally arranged here to give some idea of the interrelationships:

Classes used for general programming

DataHubConnector provides connectivity to the DataHub.

DataHubEventConsumer implements callbacks for DataHubConnector.

DataHubEventDispatcher is an interface that extends DataHubEventConsumer class, and is used by the DataHubBaseApplet class (see below).

DataHubPoint represents DataHub point objects.

Classes used for web programming

DataHubBaseApplet is the applet that makes connections to the DataHub. It provides access to all the data in a single domain. There need be only one DataHubBaseApplet per HTML page, because indivual connections are made using DataHubListener (see below). The following two classes extend the DataHubBaseApplet class:

DataHubViewer displays a table of all the data in the domain. It implements DataHubEventConsumer.

DataHubLink is used to instantiate a DataHubBaseApplet for supporting DataHubListener widgets. It embeds a small text message "Powered by Cogent" in the page, and it's color: red, yellow, or green, indicates the status of the link.

DataHubListener is an applet that gets data from a specific point or points in the DataHub. It is a parasite in the sense that it relies on the connection to the DataHub provided by a DataHubBaseApplet. You can use any number of DataHubListeners per HTML page, without noticably affecting the rate of data throughput to the page. The following three widgets are extended from DataHubListener:

DataHubLabel displays the value of a DataHub point.

DataHubEntryField is an entry field for changing the value of a DataHub point.

DataHubButton sends a value for a DataHub point.

DataHubToggleButton toggles a DataHub point between two values.

DataHubCheckBox toggles a DataHub point between two values.

DataHubRadioButton a special button, used in a DataHubRadioGroup.

DataHubRadioGroup a group of DataHubRadioButtons that provides a way to select one of several mutually-exclusive values for a DataHub point.

DataHubSlider changes the value of a DataHub point by sliding a pointer.

DataHubSpinner sets the value of a DataHub point using up and down arrows.

DataHubProgressBar gives a graphical representation of the value of a DataHub point.

DataHubDummy is provided as a convenience to the HTML programmer.

For internal use

DataHubRendezvous provides a meeting point for the DataHubBaseApplet and all of the DataHubListener widgets on the page. It is for internal use, providing static data that gets initialized before any applet starts, giving all the applets a means of finding one another.

Import Statements

import cogent.*;

import cogent.DataHubConnector;
import cogent.DataHubPoint;


1.3. C++ Programming		1.5. .NET Programming