Java applets and working principles

Java applets and working principles

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  Java Applets for begginers
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  2 Introduction to JavaApplet Programs  Applications are stand alone programs  executed with Java interpreter
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  3 Java Applets  Builtusing one of general definitions of applets  Applet class  JAapplet class  Java applets are usually graphical  Draw graphics in a defined screen area  Enable user interaction with GUI elements
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  4 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
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  5 Java Applets  Appletsare 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
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  6 Contrast Application withApplet Application Applet •Object class extended •Class not declared public •Has a main() •static keyword used •Uses System.exit(1) •JApplet class extended •class declared to be public •init() instead of main() •init() not declared with static keyword
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  7 Applet Declaration  Syntax(note difference from application declaration) public class ClassName extends JAapplet ClassName is an object that will be a subclass of JApplet
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  8 Body of anApplet  Note there is no main() method in an applet  JApplet class provides other methods instead of a main method  First method executed is the init() method
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  9 Applets  Applet  Programthat 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
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  10 Applets and WebPages – 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
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  11 Applets and WebPages – 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
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  12 Applets and WebPages – 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
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  13 Applets and WebPages – HTML  Client Web browser anywhere can access this web page from its host server  Embedded Java applet runs on client browser (of any type platform)
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  14 Thinking About Objects Java an object-oriented language  However, Java has constructs from structured programming  Object orientation  Natural way to think about world and writing computer programs • Object-oriented programming models the real world  Attributes - properties of objects • Size, shape, color, weight, etc.  Behaviors - actions that objects can perform • A ball rolls, bounces, inflates and deflates
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