Applet Initialization and termination

INITIALIZATION AND TERMINATION OF APPLET IN JAVA

APPLET INITIALIZATION AND TERMINATION

When an applet begins, sequence of methods are:
1. init( )
2. start( )
3. paint( )
When an applet is terminated, the sequence is:
1. stop( )
2. destroy( )

init( ) :

• The init( ) method is the first method to be called.
•  Initializing the variables.
•  This method is called only once during the run time of the applet.

start( ) :

• Called after init( ).
• Also called to restart an applet after it has been stopped.
• Called each time an applet’s HTML document is displayed onscreen

paint( ) :

• Called each time an applet’s output must be redrawn.
• Also called when the applet begins execution.
• The method has one parameter of type Graphics.
• This parameter will contain the graphics context, which describes the graphics environment in which the applet is running.

stop( ) :

• Called when a web browser leaves the HTML document containing the applet.
• Used to suspend threads that don’t need to run when the applet is not visible.
• We can restart them when start( ) is called.

destroy( ) :

• called when the environment determines that the applet needs to be removed completely from memory.
• The stop( ) method is always called before destroy( ).

Overriding update( ) :

• This method is called when the applet has requested that a portion of its window be redrawn.
• The default version of update( ) simply calls paint( ).
• We can override the update( ) method.

Example for nested try Statements:

// Use Parameters

import java.awt.*;

import java.applet.*;

/*

<applet code="ParamDemo" width=300 height=80>

<param name=fontName value=Courier>

<param name=fontSize value=14>

<param name=leading value=2>

<param name=accountEnabled value=true>

</applet>

*/

public class ParamDemo extends Applet{

String fontName;

int fontSize;

float leading;

boolean active;

// Initialize the string to be displayed.

public void start() {

String param;

if(fontName == null)

fontName = "Not Found";

   param = getParameter("fontSize");

try {

       if(param != null) // if not found

fontSize = Integer.parseInt(param);

       else

fontSize = 0; 

} catch(NumberFormatException e) {

fontSize = -1;

}

param = getParameter("leading");

try {

if(param != null) // if not found

           leading = 

      Float.valueOf(param).floatValue();

else

leading = 0;

} catch(NumberFormatException e) {

leading = -1;

}

param = getParameter("accountEnabled");

if(param != null)

     active = Boolean.valueOf(param).booleanValue();

}

// Display parameters.

public void paint(Graphics g) {

g.drawString("Font name: " + fontName, 0, 10);

g.drawString("Font size: " + fontSize, 0, 26);

g.drawString("Leading: " + leading, 0, 42);

g.drawString("Account Active: " + active, 0, 58);

}

}

Output: