Xlet

An Xlet is very similar to a Java applet and is designed to support applications for Digital TV as part of Sun's Java TV specification. Xlets, unlike applets, can be paused and resumed.

Xlets provision of a pause/resume feature is essential for a set-top box (STB) environment, which has limited memory resources and restrictions on bandwidth from the headend provider. The current practice and intent of the Xlet framework is to provide downloadable applications for Connected Device Configuration (CDC) platforms. In particular, the BD-J platform uses Xlets as its programming framework.

While Sun has provided a Java TV 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 {}
}