Applets, Graphical User Interfaces, and Threads / Chapter 9 1 Applets, Graphical User Interfaces, and Threads

Applets, Graphical User Interfaces, and Threads / Chapter 9 2 Interface ? an agent between two entities

Applets, Graphical User Interfaces, and Threads / Chapter 9 3 Interface

Applets, Graphical User Interfaces, and Threads / Chapter 9 4 Interface

Applets, Graphical User Interfaces, and Threads / Chapter 9 5 Interface

Applets, Graphical User Interfaces, and Threads / Chapter 9 6 Interfaces ATM machine remote control bank teller browser (Netscape Navigator or Internet Explorer) real interfaces

Applets, Graphical User Interfaces, and Threads / Chapter 9 7 Interfaces are designed to handle events initiated by user

Applets, Graphical User Interfaces, and Threads / Chapter 9 8 Events single click double click dragging

Applets, Graphical User Interfaces, and Threads / Chapter 9 9 Events An applet has mechanisms to handle events

Applets, Graphical User Interfaces, and Threads / Chapter 9 10 Applet A Java programs designed to run in a browser

Applets, Graphical User Interfaces, and Threads / Chapter 9 11 Applet applet class files are embedded in a HTML document

Applets, Graphical User Interfaces, and Threads / Chapter 9 12 all applets are subclasses of the applet class Applet public class SomeApplet extends Applet{ … }

Applets, Graphical User Interfaces, and Threads / Chapter 9 13 Applets differ from applications in that a browser controls the applet’s execution Applet

Applets, Graphical User Interfaces, and Threads / Chapter 9 14 the browser calls your applet's init() method when the applet is started. An applet's start() and stop() methods are called when the page where the applet is running gains or loses focus. Applet

Applets, Graphical User Interfaces, and Threads / Chapter 9 15 Why Restrict Applets ? An applet is code from another machine that you are not familiar

Applets, Graphical User Interfaces, and Threads / Chapter 9 16 Applet Restrictions cannot automatically send information to a user’s printer prevented from performing file operations prevented from certain network activities

Applets, Graphical User Interfaces, and Threads / Chapter 9 17 Applet Restriction Relaxed can be relaxed by changing the browser’s security settings

Applets, Graphical User Interfaces, and Threads / Chapter 9 18 Applet Syntax public class appletName extends Applet{ … }

Applets, Graphical User Interfaces, and Threads / Chapter 9 19 Sample Applet import java.applet.Applet; import java.awt.Graphics; public class Welcome extends Applet { public void paint(Graphics g){ g.drawString("Java is fuuuuuuuuuun :)...",25,25); }

Applets, Graphical User Interfaces, and Threads / Chapter 9 20 Applet’s HTML File the HTML file name does not have to match the name of the class name as in the java file however, the class name in the applet code tag must match the class name

Applets, Graphical User Interfaces, and Threads / Chapter 9 21 Applet’s HTML File the area of the applet is determined by the width and height parameters

Applets, Graphical User Interfaces, and Threads / Chapter 9 22 Applet Template import java.awt.*; import java.applet.*; public class SampleApplet extends Applet{ public void init(){ System.out.println("SampleApplet.init() executed"); } public void paint(Graphics g){ } public void start(){ } public void stop(){ } }

Applets, Graphical User Interfaces, and Threads / Chapter 9 23 Applet’s Life the browser manages the life cycle of the applet the life cycle includes the following › init › start › stop › destroy paint

Applets, Graphical User Interfaces, and Threads / Chapter 9 24 Applet Methods (init) called when an applet begins called once during the applet’s execution code to initialize the applet is placed in init()

Applets, Graphical User Interfaces, and Threads / Chapter 9 25 Applet Methods (start) called immediately after init() when the page where the applet is running gains focus

Applets, Graphical User Interfaces, and Threads / Chapter 9 26 Applet Methods (stop) called when the page where the applet is running loses focus

Applets, Graphical User Interfaces, and Threads / Chapter 9 27 Applet Methods (destroy) called when the browser terminates

Applets, Graphical User Interfaces, and Threads / Chapter 9 28 Applet Methods (paint) refreshes the browser display