If your application doesn't demand constant key presses, after a while the screen saver on a J2ME phone will start automatically.

To make sure that the display light is turned on, the setLights method should be called before the screen saver is started and this must be done in a loop since the screen saver is not disabled just interrupted.

import
 com.nokia.mid.ui.DeviceControl
;

import
 javax.microedition.lcdui.*
;

import
 javax.microedition.midlet.*
;

 
public
 class
 BacklightWorkaround extends
 MIDlet {


   private
 SimpleCanvas canvas;


   /**
   * Keeps the backlight on by repeatedly setting
   */

  class
 LightThread extends
 Thread

 {


    public
 void
 run(
)
 {

      while
(
true
)
{

        DeviceControl.setLights
(
0, 100)
;
       
        try
 {

          Thread

.sleep
(
5000)
;

        }
 catch
 
(
InterruptedException

 ex)
 {

          ex.printStackTrace
(
)
;

        }

      }

    }

  }


   private
 class
 SimpleCanvas extends
 Canvas

 implements
 CommandListener{


    private
 Command exitCmd;

    private
 MIDlet midlet;

 
    public
 SimpleCanvas(
MIDlet midlet)
 {

      this
.midlet
 =
 midlet;

      exitCmd =
 new
 Command(
"Exit"
,Command.EXIT
, 1)
;

      addCommand(
exitCmd)
;

      setCommandListener(
this
)
;

    }


    public
 void
 paint(
Graphics

 g)
 {
 
      g.drawString
(
"Let there be light."
, 0, 0, Graphics

.LEFT
|
Graphics.TOP
)
;

    }


     public
 void
 commandAction(
Command command, Displayable displayable)
 {

      if
(
command ==
 exitCmd)
{

        midlet.notifyDestroyed
(
)
;

      }

    }

  }

 
  public
 void
 startApp(
)
 {

    if
(
canvas ==
 null
)
{

      canvas =
 new
 SimpleCanvas(
this
)
;

      new
 LightThread(
)
.start
(
)
;

    }
 
    Display.getDisplay
(
this
)
.setCurrent
(
canvas)
;

  }


   public
 
void
 pauseApp(
)
 {
 }

 
  public
 void
 destroyApp(
boolean
 unconditional)
 {
 }


}

Method

Description

static void flashLights(long duration)

Flashes the lights.

static void setLights(int num, int level)

Turns the lights on and off.

static void startVibra(int freq, long duration)

Vibrates for a given frequency and time.

static void stopVibra()

Stops vibrating.

The two device elements you can control are the lights and vibration. To temporarily flash the lights on and off, use the flashLights method. For example:

import com.nokia.mid.ui.DeviceControl;
…
    DeviceControl.flashLights(5000);

This code will cause the lights (such as the LEDs) to flash. If there is no support for this feature, then nothing will happen (duh). The integer value specifies the length of time (in milliseconds) to keep the lights on, although the device might override this value if you specify a number that is too large.

The other method relating to lights, setLights , allows you to control any of the lights on the device individually, such as the backlight or the LEDs …in theory. In reality, Nokia only gives you the ability to control the device's backlight (if it has one). To do this, call the method with the light number (the first integer) set to 0 for the backlight and the level integer set to a number between 0 and 100 (where 0 is off and 100 is the brightest level). For devices that don't support graded backlighting, all values between 1 and 100 just translate to on. Here's an example of setLights in action:

DeviceControl.setLights(0, 100);