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7/28/2019 Applet Programing
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Applet Programming
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What is Applet
An applet is a special kind of Javaprogram which is used for internet
programming.
The applets reside in a server and theycan be downloaded from the server to the
client machine and executed on client
machine provided that the browser shouldbe enabled with Java technology.
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Types of Applet
Applets are basically of two types.1. Local Applet These are applets which are
created for standalone PC's where the same
PC is distinguished as server and client.
Hence, to execute a local applet there is no
need of internet connection.
2. Remote Applet The applets which are
developed for an environment where theserver and the client machine are physically
apart from each other are called remote
applets
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Needs of Applet
1. Applet is a window based application.2. Applets are basically used to create
dynamic pages.
3. The difference of an applet program froma normal program is that it does not
contain the main function. So it has no
entry point.4. The program starts executing from some
functions present in Applet class.
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Need for applet
5. an applet program cannot be executedindependently as done in case of normal
application programs.
6. They must be executed with the help ofeither applet viewer or with the help of
any web browser.
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Creating an applet program
We need to import two packages for writing anapplet program
Import java.lang.awt.*;
Import java.lang.applet.*;
The java.lang.awt.* package provides a set ofclasses and using those classes we can create awindow component and it also contains a graphicclass;
the java.lang.applet.* package is used as we areusing an applet class which is present in appletpackage.
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30Applet Class
An applet class is a member of JavaApplication Programming Interface(API)
Package.
An applet class is extended from the PanelClass, which is further extended from the
classes Container, Component and
Object. Object class is the member class of the
java.lang package and is called in the
program automatically.
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The component, container and Panelclasses are the members of java.awt
package that provide visual components
such as label,button and text fields. Anapplet is the only member of the
java.applet package.
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30Java Class Hierarchies
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10
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30Abstract windows Toolkit(AWT)
The awt package is a collection of classesand methods that allow an end user to
design and manage graphical user
interface(GUI) based application. AWT is used to support applet windows
and it also helps in creating independent
windows such as frame window or panelwindow that run in GUI environment.
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30Abstract windows Toolkit(AWT)
AWT is javas Largest Package that canbe included in java program by giving the
java.awt.* statement.
It is a part of java foundation classes(JFC). AWT has 63 classes and 14 interfaces
used for creating user interfaces.
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30Features of the AWT package
It provides graphics and imaging tools thatenable you to develop GUI.
It provides layout manager that enables an
end user to develop window layouts. It supports event handling. for example, an
error occurred in between execution of a
program.
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13
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30Hierarchy of java.awt package
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30Component Class
Component class is at the top of the AWTinheritance class hierarchy. It is the super
class and all others in the hierarchy inherit
its characteristics directly or indirectly. Component class is the abstract class that
encapsulated all the properties of visual
components or object.
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30Methods of the component class
void setSize(int width, int height): definesthe size of a component in terms of wisth and
size.
void setLocation(int x,int y): specifies thelocation of a components, in the window, at the
position specified by the x and y coordinates.
void setBounds(int x,int y,int width ,intheigth): sets the bounds of a component in
terms of position x and y and size in terms of
width and height.
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Void setForeground(Color b): sets theforeground color of the component.
Void setBackground(Color b): sets the
background color of the component.
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Container class is the subclass of component
class.
Methods that are used to manipulate
components on container objects are:
void add(object o): Nest a Component or an
object inside a container.
void remove(object o): removes a component
or an object from a container.
void removeALL(): removes all the
components or objects that are placed inside a
container.
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When we want to execute an applet programwith the help of a web browser, we need to
write an HTML file.
ExampleofApplet
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Applet Programming
importjava.lang.awt.*;importjava.lang.applet.*;publicclassmessageextendsApplet
{
Stringmsg;publicvoidinit()
{
msg=Welcometoappletprogramming;
}
publicvoidpaint(Graphicsg)
{ g.drawString(msg,100,400); }}
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R i th l t i W b b
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Running the applet in a Web browser
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APPLET LIFE CYCLE
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Applet Life Cycle
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Applet
Public keyword is used because we run anapplet program in a media different from
that in which we write it.
Paint() method used in the above examplecalls drawString() function which is a
function of Graphics class.
Applet class contains certain functions likeinit(), start(), stop(), paint(), destroy(), etc.
which are usually used in programs.
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Method init()
init() methodWhenever an applet isloaded into a web page this method is
automatically called. This method provides
an appropriate place for initialization of thevariables required and other set up
operations such as setting of background
color, defining the applets layout, parsing
parameters, etc.
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Method start()
start() method After the initialization iscompleted, start() method is called.
The difference between this method and the
init() method is that init() method is calledonly when the page is loaded, whereas
start() method is called every time the page
is loaded and every time the page is
restarted.
This method is mainly used while
implementing threads in Java.
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Method stop()
stop() method This method is calledwhenever the user navigates from one
page to another page.
It is always advisable to use stop()method if any type of animation or memory
consuming activities is being performed in
order to avoid wasting of systemresources.
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Method destroy()
destroy() method This method is calledimmediately before the applet exits.
The exiting operation is caused by either
the applet operation requesting for the exitor may be the web browser is shut down.
When it is called it directs the applet to
free up all the system resources beingused by it.
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Methods in applet
/* */
import java.awt.*;
import java.applet.*;public class balli1 extends Applet
{
String str="Hello ";
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30Methods in applet
public void init(){
str=str+"";
}
public void start()
{
str=str+" ";
}
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30Methods in applet
public void stop(){
str=str+"";
}
public void destroy()
{
str=str+"";
}
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30Methods in applet
public void paint(Graphics g){
str=str+"";
g.drawString(str,50,50);
}
}
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30Out Put of the Program
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1. http://aspalliance.com/1309_Introducing_Java_Applets.1
2. The Complete Reference by Patrick Naughton and Herbert Schildt
36
http://aspalliance.com/1309_Introducing_Java_Applets.1http://aspalliance.com/1309_Introducing_Java_Applets.17/28/2019 Applet Programing
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The End
Thanks