Applet and graphics programming
- 2. Applet Programming • Applets are small Java programs that are primarily used in Internet computing. • They can be transported over the Internet from one computer to another and run using the Applet Viewer or any Web browser that supports Java. • An applet, like any application program, can do many things for us. It can perform arithmetic operations, display graphics, play sounds, accept user input, create animation, and play interactive games.
- 3. Local and Remote Applets • An applet developed locally and stored in a local system is known as a local applet. • A remote applet is that which is developed by someone else and stored on a remote computer connected to the Internet. • In order to locate and load a remote applet, we must know the applet’s address on the Web. This address is known as Uniform Resource Locator(URL).
- 4. How Applets differ from Applications • Applets do not use the main() methods for initiating the execution of the code. • Unlike stand-alone applications, applets cannot be run independently. They are run from inside a Web page using a special feature known as HTML tag. • Applets cannot read from or write to the files in the local computer. • Applets cannot communicate with other servers on the network. • Applets cannot run any program the local computer. • Applets are restricted form using libraries form other languages such as C or C++.
- 5. To Write Applets • Building an applet code (.java file) • Creating an executable applet (*.class file) • Designing a Web page using HTML tags • Preparing <APPLET> tag • Incorporating <APPLET> tag into the Web page • Creating HTML file • Testing the applet code
- 6. Chain of classes inherited by Applet Class java..lang.Object java.applet.Applet java.awt.Panel java.awt.Container java.awt.Component
- 7. Applet Life Cycle • The applet states include: – Born or initialization state – Running state – Idle state – Dead or destroyed state
- 8. Born Running Idle Dead Begin (Load Applet) Initalization Start( ) stop( ) start( ) Stopped destroy ( ) EndDestroyed Exit of Broswer paint ( ) Display An applet’s state transition diagram
- 9. Applet Life Cycle • Initialization State – Applet enters the initialization state when it is first loaded. This is achieved by calling the init( ) method of Applet Class. – The applet is born. – The initialization occurs only once in the applets’life cycle. – To provide any of the behaviours mentioned above, we must override the init ( ) method: public void init( ) { //statements }
- 10. • Running State – Applet enters the running state when the system calls the start ( ) method of Applet Class. – The occurs automatically after the applet is initialized. – Starting can also occur if the applet is already in “stopped” (Idle ) state. – Unlike init( ) method, the start ( ) method may be called more than once. public void start() { // statements } Applet Life Cycle
- 11. • Idle or Stopped State – An applet becomes idle when it is stopped from running. Stopping occurs automatically when we leave the page containing the currently running applet. public void stop( ) { //statements } Applet Life Cycle
- 12. • Dead State – An applet is said to be dead when it is removed from memory. This occurs automatically by invoking the destroy ( ) method when we quit the browser. – Like initialization, destroying stage occurs only once in the applet’s life cycle. public void destroy( ) { //statements } Applet Life Cycle
- 13. • Display state – Applet moves to the display state whenever it has to perform some output operations on the screen. – This happens immediately after the applet enters into the running state. – The paint( ) method is called to accomplish this task. – Almost every applet will have a paint( ) method. – Paint( ) method is inherited form the Component class , a super class of Applet. public void paint (Graphics g) { //statements } Applet Life Cycle
- 14. import java.awt.*; import java.applet.*; public class HelloJava extends Applet { public void paint(Graphics g) { g.drawString("Hello Java",10,100); } } <html> <body> <applet code = "HelloJava.class" height=“100” width =“200”> </applet> </body></html>
- 15. Applet Tag • The <Applet. .>tag supplies the name of the applet to be loaded and tells the browser how much space the applet requires. • <APPLET> tag specifies three things: – Same of the applet – Width of the applet (in pixels) – Height of the applet (in pixels)
- 16. Passing Parameters to Applets • We can supply user-defined parameters to an applet using <PARAM…> tags. • Each <PARAM…>tag has a name attribute such as color and a value attribute such as red. • Inside the applet code, the applet can refer to that parameter by name to find its value. • To set up and handle parameters, we need to do two things: – Include appropriate <PARAM…> tags in the HTML document – Provide Code in the applet to parse these parameters. • Parameters are passed to an applet when it is loaded. We can define the init() method in the applet to get hold of the parameters defined in the <PARAM> tags. • This is done using the getParameter( ) method, which takes one string argument representing the name of the parameter and returns a string containing the value of the parameter.
- 17. import java.awt.*; import java.applet.*; public class JavaParam extends Applet { String s; public void init() { s = getParameter("uname"); if(s==null) s = “ABC”; s = "Hello" + s; } public void paint(Graphics g) { g.drawString(s,10,100); } } <html> <body> <APPLE CODE = JavaParam.class width=400 height = 200> <PARAM NAME = "uname" VALUE="ruchita"> </APPLE> </body> </html>