An Xlet is very similar to a Java applet

Java applet

A Java applet is an applet delivered to users in the form of Java bytecode. Java applets can run in a Web browser using a Java Virtual Machine , or in Sun's AppletViewer, a stand-alone tool for testing applets...

 and is originally introduced in Sun's Java TV

Java TV

Java TV is a Java-based software framework designed for use on TV set-top boxes, based around components called Xlets. It is currently used only on the Connected Device Configuration, specifically for iTV applications development....

 specification to support applications for Digital TV. Though Xlet looks superficially different from other application models in Java such as applet and MIDlet

MIDlet

A MIDlet is an application that uses the Mobile Information Device Profile of the Connected Limited Device Configuration for the Java ME environment...

, it is actually meant to be a generalization of such models. X in Xlet means an unknown, meaning Xlet may be used in any context rather than specific to Digital TV. Accordingly Xlet has later been re-introduced as a part of Personal Basis Profile in javax.microedition.xlet package, which is slightly different from the original design in Java TV specification.

Xlets provision of a pause/resume feature is essential for a set-top box

Set-top box

A set-top box or set-top unit is an information appliance device that generally contains a tuner and connects to a television set and an external source of signal, turning the signal into content which is then displayed on the television screen or other display device.-History:Before the...

 (STB) environment, which has limited memory resources and restrictions on bandwidth

Bandwidth (computing)

In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...

 from the headend

Cable television headend

A cable television headend is a master facility for receiving television signals for processing and distribution over a cable television system. The headend facility is normally unstaffed and surrounded by some type of security fencing and is typically a building or large shed housing electronic...

 provider. The current practice and intent of the Xlet framework is to provide downloadable applications for Personal Basis Profile (PBP) platforms. In particular, the BD-J

BD-J

BD-J, or Blu-ray Disc Java, is a specification supporting Java ME Xlets for advanced content on Blu-ray Disc and the Packaged Media profile of Globally Executable MHP .BD-J allows bonus content on Blu-ray Disc titles to be far more sophisticated than bonus content provided by standard DVD,...

 platform uses Xlets as its programming framework.

While Sun has provided a Java TV

Java TV

Java TV is a Java-based software framework designed for use on TV set-top boxes, based around components called Xlets. It is currently used only on the Connected Device Configuration, specifically for iTV applications development....

reference implementation within which they provide a simple Xlet runner called RunXlet, at least one other open-source effort to implement an Xlet run has been made.

Code examples

The interface for an Xlet is defined in the javax.tv.xlet package:


public interface Xlet {
public void initXlet(XletContext ctx)
throws XletStateChangeException;

public void startXlet
throws XletStateChangeException;

public void pauseXlet;

public void destroyXlet(boolean unconditional)
throws XletStateChangeException;
}


thus an example of a stub Xlet is


import javax.tv.xlet.XletStateChangeException;
import javax.tv.xlet.XletContext;
import javax.tv.xlet.Xlet;

public class BasicXlet implements Xlet {
public BasicXlet {}
public void initXlet (XletContext context) throws XletStateChangeException {}
public void startXlet throws XletStateChangeException {}
public void pauseXlet {}
public void destroyXlet (boolean unconditional) throws XletStateChangeException {}
}