Java Programming- Introduction to Java Applet Programs

Java Programming- Introduction to Java Applet Programs

• 1.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Affiliated Institution of G.G.S.IP.U, Delhi BCA Java Programming BCA - 206 Java Applets Keywords: applet, JApplet, Swing
• 2.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Introduction to Java Applet Programs • Applications are stand alone programs – executed with Java interpreter • Applet is a small program – can be placed on a web page – will be executed by the web browser – give web pages “dynamic content”
• 3.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Java Applets • Built using one of general definitions of applets – Applet class – JApplet class • Java applets are usually graphical – Draw graphics in a defined screen area – Enable user interaction with GUI elements
• 4.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Java Applet Classes Abstract Windowing Toolkit AWT Earlier versions of Java Applet class is one of the AWT components Java Foundation Classes JFC Extension to Java in 1997 Has a collection of Swing components for enhanced GUIs Swing component classes begin with J
• 5.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Java Applets • Applets are Java programs that can be embedded in HTML documents – To run an applet you must create a .html file which references the applet – Ready to Program also will run an applet • When browser loads Web page containing applet – Applet downloads into Web browser – begins execution • Can be tested using appletviewer program
• 6.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Contrast Application with Applet Application • Object class extended, Class not declared public, Has a main(), static keyword used, Uses System.exit(1) Applet • JApplet class extended, class declared to be public, init() instead of main(), init() not declared with static keyword
• 7.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Applet Declaration Syntax (note difference from application declaration) public class ClassName extends JAapplet ClassName is an object that will be a subclass of JApplet
• 8.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Body of an Applet There is no main() method in an applet JApplet class provides other methods instead of a main method First method implemented is the init() method
• 9.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Applets • Applet –Program that runs in • appletviewer (test utility for applets) • Web browser (IE, Communicator) –Executes when HTML (Hypertext Markup Language) document containing applet is opened –Applications run in command windows
• 10.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Applets and Web Pages – HTML • Applets embedded in a web page – Executed when web page loaded by browser • Web pages structured with HTML codes –HyperText Mark-up Language • Syntax <command> . . . </command> Turns format on Turns the format off Turns format on Turns the format off
• 11.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Applets and Web Pages – HTML • Embedding Java applets – Insert applet tags <APPLET> </APPLET> • Call the specific applet by its file name <APPLET CODE = "Whatever.class" WIDTH = nnn HEIGHT = mmmm> <APPLET> Where nnn and mmm are specific pixel sizes
• 12.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Applets and Web Pages – HTML Create the web page code using a text editor Save it with an .html suffix Open this file with appletviewer or with a web browser that supports Java Java Plug-in must be installed (part of J2SDK 1.4.1 from Sun) <HTML> <HEAD> </HEAD> <BODY> <APPLET CODE = . . . > </APPLET> </BODY> </HTML>
• 13.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 • Client Web browser anywhere can access this web page from its host server • Embedded Java applet runs on client browser (of any type platform) • This means a client anywhere on any type of platform can run a piece of software developed on any other type of platform Applets and Web Pages – HTML
• 14.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 A Simple Java Applet: Drawing a String
• 15.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Running the Applet • Save this file as WelcomeApplet.java • Compile this program –If no errors, bytecodes stored in WelcomeApplet.class
• 16.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Running An Applet Now Create an HTML file indicating which applet the browser (or appletviewer) should load and execute • Save it as WelcomeApplet.html • Make sure you save it in the same directory as the .java file <html> <applet code = “WelcomeApplet.class" width=275 height = 100> </applet> </html>
• 17.
  TRINITY INSTITUTE OFPROFESSIONAL STUDIES Sector – 9, Dwarka Institutional Area, New Delhi-75 Running An Applet • To execute an applet, either run the html file on java enabled web browser or run the following command at command prompt appletviewer WelcomeApplet.html The output :