Applets & Applications CSC 171 FALL 2001 LECTURE 15

History: Grace Hooper 1952 Grace Hopper working on the UNIVAC, "The Education of a Computer", (Proc. ACM Conference) The use of selected pre-written code segments to be assembled into programs written in a high level language The concept of a compiler, and the general concept of language translation.

Applets & Applications Generally run over networks Code download Client side execution Extend Applet Applications Generally run on hosts Resident host Local host execution Extend Frame

GUIs in general Sometimes, it is useful to have a program that runs as either an applet or an application

Applet/App Architecture Button Handler actionListener Applet actionPerformed() DrawShapes JPanel setWidth() init() DrawPanel setHeight() main() setcurrentchoice() paintComponent()

Relationships DrawShapes DrawPanel is-a Jpanel is-a Applet has-a Jframe (inside of main) Has-a DrawPanel Has-a ButtonHandler DrawPanel is-a Jpanel ButtonHandler implements ActionListener

What Happens In an Applet? JVM calls DrawShapes.init() Builds DrawPanel Builds ButtonHandler BuildsButtons Adds components

What Happens In an Application? JVM calls DrawShapes.main() Builds Jframe application window Builds DrawShapes Applet (see previous) Calls DrawShapes.init() Calls DrawShapes.start. Adds applet to application window I.E. (har) : Frame takes place of browser

Using Command Line Args public static void main( String args[] ){ int width, height; // check for command-line arguments if ( args.length != 2 ) { width = 300; height = 200; } else { width = Integer.parseInt( args[ 0 ] ); height = Integer.parseInt( args[ 1 ] );

Build the Application // create window in which applet will execute JFrame applicationWindow = new JFrame( "An applet running as an application"); applicationWindow.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

Build the applet from the application // create one applet instance DrawShapes appletObject = new DrawShapes(); appletObject.setWidth( width ); appletObject.setHeight( height ); // call applet's init and start methods appletObject.init(); appletObject.start();

Get it going // attach applet to center of window applicationWindow.getContentPane().add( appletObject ); //note nested method calls applicationWindow.setSize( width, height ); applicationWindow.setVisible( true );

Architecture of Applet Separate class for button handler Separtae class for drawing region Separate button panel & Draw panel Applet is in BorderLayout NORTH Panel containing grid layout with 3 buttons CENTER Drawing region

ButtonHandler private class ButtonHandler implements ActionListener { // can access choices because it is an inner class public void actionPerformed( ActionEvent event ) { for ( int count = 0; count < choices.length; count++ ) if ( event.getSource() == choices[ count ] ) { drawingPanel.setCurrentChoice( count ); break; } } // end private inner class ButtonHandler

DrawPanel Using a separate panel allows painting without interfering with other components Loosely coupled with Applet No shared data

When ButtonHandler invokes setCurrentChoice() // specify current shape choice and repaint public void setCurrentChoice( int choice ) { currentChoice = choice; repaint(); }

DrawPanel public void paintComponent( Graphics g ) { super.paintComponent( g ); switch( currentChoice ) { case 0: g.drawLine( randomX(), randomY(), randomX(), randomY() ); break; //etc. . . . } } // end method paintComponent