Building Applications and Applets 
Applications require a main method: 
public static void main( String[] args ) 
Applets require a public constructor: 
public classname( ) 
To make an application work as an applet too, write the main method to use 
  MainFrame 
public static void main( String[] args )	{
   new MainFrame( new HelloUniverse( ), 640, 480 );
}