interactive java note - m06_un11_p01

8/3/2019 Interactive Java Note - M06_UN11_P01

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Programming Language (JAVA)

Unit 6.11 Applets

Presentation1


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Revision

1. Explain exception handling in Java.

2. List the types of exceptions in Java

language.

3. What are try, catch and throw blocksused for?


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Objectives

At the end of this presentation, you will be able to :

Explain applet programming

List the differences between applications andapplets

Describe the different stages in the life cycle ofan applet


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Java Programs

Java supports two kinds of programs.

Java Applications are the normal standalone

programs.

Java Applets are the programs that are to beembedded in a Web page.


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Applet Programming

Appletsare the Java programs that areexecuted by the Web browser.

Appletviewer is a Java utility to executeapplets.

Applet is a special class file written to display

graphics in a Web browser.


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Applets

Applets are embedded in Web pages usingthe HTML tag .

When a Web page containing applet programis run, it is downloaded to the memoryautomatically and executed by the Webbrowser.

Applet gets displayed in the specific spaceallocated in the Web page called AppletWindow.


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Applets

Applets can contain embedded objects like :

Animated graphics

Video games

Advanced text displays and images

Audio


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Applet Types

Local Applets

Applets that are stored in the local machine

Remote Applets

Applets that are stored in a remote computer.

These can be downloaded and embedded into Web

pages from the Internet.


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Local Applets


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Remote Applets


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Applets Vs. Applications

Applets Applications

Applets are embedded in

Web pages and cannot be runindependently.

Applications can be

run independently.

Applet programs call certain

methods such as init(),

start(),stop(), and destroy()of Applet class to start andexecute the applet code.

Programs use the

main() method for

initiating theexecution of thecode.


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Applets Vs. Applications (Contd..)

Applets Applications

Applets cannot read from or

write to the files in the localcomputer.

Applications can

read from or writeto local computer.

Applets enable the user tointeract graphically.

Applications do notenable the user to

interact graphically.


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Life Cycle of Applets

The four methods executed are :

1. init()

2. start()

3. stop()

4. destroy()


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Life Cycle of Applets


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init()

Initialisation State

This method is executed when it is first

loaded into the memory.

The applet is now said to exist in the

initialisation state.


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init()

Syntax

public void init( )

{

;

}


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start()

Running State

The start()method of the Applet Class isexecuted whenever an applet is started orrestarted.

The applet is now said to exist in the running

state.


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start()

Syntax

public void start()

{

;

}


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stop()

Idle State

The stop() method is executed when anapplet is closed.

The applet is stopped automatically when theuser switches to another program or Webpage.

This can also be done by invoking explicitlythe stop() method of Applet class.

When this is invoked the applet enters the

idle state.


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stop()

Syntax

public void stop( )

{

;

}


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destroy()

Dead State

The destroy() method is executed when a

Web page is closed.

The applet is now said to be in the deadstate.


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destroy()

Syntax

public void destroy( )

{

;

}


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paint()

Thepaint()method of the Applet class isexecuted automatically whenever the applet

is displayed in the Web page. This method is used to draw graphics in the

drawing area of the applet.


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repaint()

The repaint() method is used whenever youwant to redraw the applets drawing area.

The repaint() method calls the update()method.

The update() method clears the applet area

and calls thepaint() method.


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paint()

Syntax

public void paint(Graphics g)

{

;

}


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Summary

In this presentation, you learnt the following

Applets are Java programs mainly used in

Internet computing.

The applets output is displayed within asubset of the display area of the browser.

Java applet inherits a set of defaultproperties from the Applet class.

An applet enters the Initialisation state when

it is first loaded.


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Summary

In this presentation, you learnt the following

Applet enters the running state when the start()method of Applet class is invoked.

An applet becomes idle when it is stopped fromrunning.

An applet is said to be dead when it is removedfrom memory.


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Assignment

1. Define an applet. List the uses of applets.

2. Sketch and explain the life cycle of anapplet.

interactive java note - m06_un11_p01

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