1 Applications & Applets Standalone applications & Java applets Peter Mozelius DSV/UCSC

2 Running Java  Standalone applications  Like traditional programs  BUT platform independent javac MyClass.java java MyClass ing/Programming/BasicJava1/compile.html ing/Programming/BasicJava1/compile.html

3 Running Java on the Internet  Applications could be packed as jar- archives and executed by JNLP  Run on a server

4 Running Java on the Internet  Two other alternatives Servlets  Running on the server side Applets  Running in the web browser  And Java Applets is the main theme for this course !!

5 Inheritance for Applets  An Object extended to  A Container extended to  A Panel that is extended to  An Applet which I can extend to  to MyApplet

6 Application  Applet How to make an applet out of an application ? THE APPLICATION: import java.awt.BorderLayout; import java.awt.event.*; import javax.swing.*; public class MyApplication extends JFrame implements ActionListener {

7 The Application private JButton northButton; private JLabel southLabel; /** * The constructor that creates the GUI */ public MyApplication(){ //set the title and the size super("Lektion24"); setSize(300, 150);

8 The Application //create some Swing components northButton = new JButton("PUSH ME for a greeting"); southLabel = new JLabel("Here goes the greeting!", JLabel.CENTER); //connect the button with a listener northButton.addActionListener(this);

9 The Application //lay out the components add(northButton, BorderLayout.NORTH); add(southLabel, BorderLayout.SOUTH); //make the window visible and closable setVisible(true); setDefaultCloseOperation(EXIT_ON_CLOSE); }//constructor

10 The Application /** * The implementation of the method from the * interface ActionListener. The code that’s * going to be executed when the user clicks * on the button */ public void actionPerformed(ActionEvent e) { southLabel.setText("Hello Colombo!"); }//actionPerformed public static void main(String[] args) { new MyApplication(); }

11 Workshop Pause

12 The Applet run by AppletViewer

13 The Applet Code part 1  Even simpler than the application import java.awt.BorderLayout; import java.awt.event.*; import javax.swing.*; import java.applet.*; public class MyApplet extends JApplet implements ActionListener {

14 The Applet Code part 2 private JButton northButton; private JLabel southLabel; /** * A method that initiates the applet and * creates the GUI */ public void init(){ //set the size of the window setSize(300, 150);

15 The Applet Code part 3 northButton = new JButton("PUSH ME for a greeting"); southLabel = new JLabel("Here goes the greeting!", JLabel.CENTER); //connect the button with a listener northButton.addActionListener(this); add(northButton, BorderLayout.NORTH); add(southLabel, BorderLayout.SOUTH); }//constructor

16 The Applet Code part 4 /** * The implementation of the method from * ActionListener. The code that is * going to be executed when the user * clicks on the button */ public void actionPerformed(ActionEvent e) { southLabel.setText("Hello Colombo!"); }//actionPerformed }//MyApplet

17 The (oversimplified) HTML file <applet code="MyApplet.class" width="300" height="200"> Problems with the applet

18 Workshop Pause

19 Another Simple Applet  A simple but  illustrative  Applet  Run with the AppletViewer

20 The Simple Applet Code 1 import java.applet.Applet; import java.awt.Graphics; import java.awt.Color; public class SimpleApplet extends Applet{ private String text;

21 The Simple Applet Code 2 public void init() { text = "I'm a simple applet"; setBackground(Color.cyan); } public void start() { System.out.println("starting..."); }

22 The Simple Applet Code 3 public void stop() { System.out.println("stopping..."); } public void destroy() { System.out.println("preparing to unload..."); }

23 The Simple Applet Code 4 public void paint(Graphics g){ g.setColor(Color.blue); g.drawRect(0, 0, getSize().width -1, getSize().height -1); g.setColor(Color.red); g.drawString(text, 15, 25); }//paint }//SimpleApplet

24 The Simple Applet Code 5  Further info about this applet can be found on: aining/Programming/BasicJava1/applet. html#struct aining/Programming/BasicJava1/applet. html#struct  In Swing applets you replace paint() with the newer paintComponent()

25 The Appletviewer  How to run applets outside a web browser

26 The Appletviewer  The final result in a web browser  A web browser works with a cache  Appletviewer during the development of the applet That all for now, thank you!