Java Applet Basics

 

Java Applet Basics

 

Java applets,however,run from inside a world wide web browser. a reference to an applet is embedded in a webpage using a special HTML tag.

Because java applets run inside a java browser,they have the advantage of the structure the browser provides: an existing window,an event-handling and graphics context,and the surrounding user interface.

Java applets can be downloaded from anywhere and run on a client's system ,restrictions are necessary to prevent an applet from causing system damage or security breaches.

some of the restrictions on applet can be as following

·      applets can't read or write to the reader's file system,except in specific directories.some browsers may not even allow an applet to read or write to the file system at all

·      applets can't communicate with a server other than the one that had originally stored the applet.

·      applets can't run any program on the reader's system.for Unix system.

·      applets can't load program native to the local platform,including shared libraries such as DLLs

EXAMPLE :1

open a new file in he editor and type the following code.

File name: MyFirstApplet.java

import java.awt.*;

public class MyFirstApplet extends java.applet.Applet{

public void paint(Graphics g){

g.drawString("My first java applet",70,30);

}

}

/*

<applet CODE="MyFirstApplet.class" WIDTH=400 HEIGHT=400></applet>

*/

·      save this file,as My FirstApplet.java and compile it using javac.this will result in the creation of a class file for the same

·      now create on HTML file and within its body,type

Output

 

 

Passing Parameter to Applet

File name: BarChart.java

import java.awt.*;

import java.applet.*;

public class BarChart extends Applet

{

int n=0;

String label[];

int value[];

public void init()

{

try

{

n=Integer.parseInt(getParameter("coloumn"));

label=new String[n];

value=new int[n];

label[0]=getParameter("label1");

label[1]=getParameter("label2");

label[2]=getParameter("label3");

label[3]=getParameter("label4");

value[0]=Integer.parseInt(getParameter("c1"));

value[1]=Integer.parseInt(getParameter("c2"));

value[2]=Integer.parseInt(getParameter("c3"));

value[3]=Integer.parseInt(getParameter("c4"));

}

catch(NumberFormatException e){}

}

public void paint(Graphics g)

{

for(int i=0;i<n;i++)

{

g.setColor(Color.red);

g.drawString(label[i],20,i*50+30);

g.fillRect(50,i*50+10,value[i],40);

}

}

}

/*<applet code="BarChart.class" width=300 Height=250>

<param name="coloumns" value="4">

<param name="c1" value="110">

<param name="c2" value="150">

<param name="c3" value="100">

<param name="c4" value="170">

<param name="label1" value="91">

<param name="label2" value="92">

<param name="label3" value="93">

<param name="label4" value="94">

</applet>

*/

Output

 

PASSING PARAMETERS TO APPLET

Testing the Result

An Applet Architecture

init()

The init() method is the first method to be called. This is where you should initialize variables. This method is called only once during the run time of your applet.

start()

The start() method is called after init(). It is also called to restart an applet after it has been stopped. Whereas init() is called once the first time an applet is loaded start() is called

Paint()

The paint() method is called each time your applet's output must be redrawn.

Stop()

The stop() method is called when a web browser leaves the HTML document containing the applet

The repaint() Method

Repaint () can be done mentioning time in miliseconds to be performed in future.

  The  Graphics Class

import java. awt. Graphics;

public class MyClass extends java.applet.Applet{

...

}

Lines

File name: Lines.java

import java.awt.*;

import java.applet.*;

/*

<applet code="Lines" width=300 height=200>

</applet>

*/

public class Lines extends Applet{

public void paint(Graphics g){

g.drawLine(0,0,100,100);

g.drawLine(0,100,100,0);

g.drawLine(40,25,250,180);

g.drawLine(75,90,400,400);

g.drawLine(20,150,400,40);

g.drawLine(5,290,80,19);

}

}

Output

 

Rectangles

The java graphics primitives provide not just one, but three kinds of rectangles:

v Plain rectangles

v Rounded rectangles, which are rectangles with rounded corners

v Three-dimensional rectangles, which are drawn with a shaded border

Rounded Rectangles

Rectangles

File name: Rectangles.java

import java.awt.*;

import java.applet.*;

/*

<applet code="Rectangles" width=300 height=200>

</applet>

*/

public class Rectangles extends Applet{

public void paint(Graphics g){

g.drawRect(10,10,60,50);

g.fillRect(100,10,60,50);

g.drawRoundRect(190,10,60,50,15,15);

g.fillRoundRect(70,90,140,100,30,40);

}

}

Output

 

Rounded Rectangles

void drawRoundRect(int top, int left, int width, int height, int)

                                                                                            xdiam, int y diam

void fillRoundRect (int top,int left, int width, int height, int

                                                                                            xdiam, int y diam

public void paint(Graphics g){

g. draw Rect(20,20,60,60);

g.fil Rect(120,20,60,60);

}

 

 

The following applet draws several  rectangles:

public void paint(Graphics g){

       g. draw Roun Rect (20,20,60,6010,10);

        g.fillRound Rect(120,20,60,60,20,20);

}

Three Dimensional Rectangles

draw 3DRect(int x1, int y1, int width,int height, true/false).

rectangles.public void paint(Gra[hics g){

   g.draw 3DReact(20,20,60,60,true);

    g.draw 3DReact(120,20,60,60,false);

}

Polygons

draw polygon (int x[], int y[],int jun points)

fil Polygon (int x[], int y[],int jun points) 

Polygon

File name: HourGlass.java

import java.awt.*;

import java.applet.*;

/*

<applet code="HourGlass" width=230 height=210>

</applet>

*/

public class HourGlass extends Applet{

public void paint(Graphics g){

int xpoints[]={30,200,30,200,30};

int ypoints[]={30,30,200,200,30};

g.drawPolygon(xpoints,ypoints,5);

}

}

Output

 

 

Ovals

File name: Ellipses.java

import java.awt.*;

import java.applet.*;

/*

<applet code="Ellipses" width=300 height=200>

</applet>

*/

public class Ellipses extends Applet{

public void paint(Graphics g){

g.drawOval(10,10,50,50);

g.fillOval(100,10,75,50);

g.drawOval(190,10,90,30);

g.fillOval(70,90,140,100);

}

}

Output

 

Arc

draw Are (int top, int left, int width, int height,int start angle, int                                                             sweep angle)

fillAre(int top, int left, int width, int height,int start angle, int                                                          sweep angle)

File name: Arcs.java

import java.awt.*;

import java.applet.*;

/*

<applet code="Arcs" width=300 height=200>

</applet>

*/

public class Arcs extends Applet{

public void paint(Graphics g){

g.drawArc(10,40,70,70,0,75);

g.drawArc(100,40,70,70,0,75);

g.drawArc(10,100,70,80,0,175);

g.fillArc(100,100,70,90,0,270);

g.drawArc(200,80,80,80,0,180);

g.fillArc(70,40,50,80,0,90);

}

}                                                                                    

Output

 

 Lamp

File name: Lamp.java

import java.awt.*;

/*

<applet code="Lamp" width=300 height=200>

</applet>

*/

public class Lamp extends java.applet.Applet{

public void paint(Graphics g){

g.fillRect(0,250,290,290);

g.drawLine(125,250,125,160);

g.drawLine(175,250,175,160);

g.drawArc(85,157,130,50,-65,312);

g.drawArc(85,87,130,50,62,58);

g.drawLine(85,177,119,89);

g.drawLine(215,177,181,89);

g.fillArc(78,120,40,40,63,-174);

g.fillOval(120,96,40,40);

g.fillArc(173,100,40,40,110,180);

}

}

Output

Creating Font Objects

Creating Font Objects

Font f = new Font("Time Roman",Font,BOLD,24);

Font methods

Name	In Object	Action
GetFont()	Graphics	Returns the current font object as previously set by
GetName()	Font	Returns the name of the font as a string
getSize()	Font	returns the current font  size (an integer)
GetStyle()	Font	Returns the current style of the font (stryle are integer constants: o is plain, 1 is bold,2 is italic,3 is bold italic)
isPlain()	Font	Return true or false if the font's styleis plain
is Bold()	Font	Returns true or false if the font's style is bold
isItalic()	Font	Returns true or false if the font's style is italic

 

Fontf=new Font("TimesRoman",Font.BOLD,36);

Font Metrics fmetrics = get FontMetrics(f);

g.setfont(f); 

File name: ManyFonts.java

/*<applet code="ManyFonts" width=300 height=300>

</applet>

*/

import java.awt.*;

import java.awt.Font;

import java.awt.Graphics;

public class ManyFonts extends java.applet.Applet{

public void paint(Graphics g){

Font f=new Font("TimesRoman",Font.PLAIN,18);

Font fb=new Font("TimesRoman",Font.BOLD,18);

Font fi=new Font("TimesRoman",Font.ITALIC,18);

Font fbi=new Font("TimesRoman",Font.BOLD+Font.ITALIC,18);

g.setFont(f);

g.drawString("This is a plain font",10,25);

g.setFont(fb);

g.drawString("This is a bold font",10,50);

g.setFont(fi);

g.drawString("This is an italic font",10,75);

g.setFont(fbi);

g.drawString("This is a bold italic font",10,100);

}

}

Output

Font Metrics Methods

File name: FontMetricsDemo.java

import java.applet.*;

import java.awt.*;

import java.awt.Font;

import java.awt.FontMetrics;

/*

<applet code=FontMetricsDemo width=300 height=300>

</applet>

*/

public class FontMetricsDemo extends Applet{

Font f1,f2;

int ascent,descent,height,leading;

String one,two,three,four;

public void init(){

f1=new Font("Helvetica",Font.BOLD,14);

f2=new Font("TimesRoman",Font.BOLD+Font.ITALIC,12);

}

public void paint(Graphics g){

g.setFont(f1);

ascent=g.getFontMetrics().getAscent();

descent=g.getFontMetrics().getDescent();

height=g.getFontMetrics().getHeight();

leading=g.getFontMetrics().getLeading();

one="Ascent of font f1 is: "+ascent;

two="Descent of font f1 is: "+descent;

three="Height of font f1 is: "+height;

four="Leading of font f1 is: "+leading;

g.drawString(one,20,20);

g.drawString(two,20,50);

g.drawString(three,20,80);

g.drawString(four,20,110);

}

}

Output

Font Metrics

File name: Centered.java

import java.awt.*;

import java.applet.*;

import java.awt.Graphics;

import java.awt.Font;

import java.awt.FontMetrics;

/*

<applet code=Centered width=300 height=300>

</applet>

*/

public class Centered extends java.applet.Applet{

public void paint(Graphics g){

Font f=new Font("TimesRoman",Font.PLAIN,36);

FontMetrics fm=getFontMetrics(f);

g.setFont(f);

String s="This is how the world ends.";

int xstart=(size().width-fm.stringWidth(s))/2;

int ystart=(size().height+fm.getHeight())/2;

g.drawString(s,xstart,ystart);

}

}

Output

Color

Color

 

Using Color Objects

 

Standard colors

 

Color  Name	RGB Value
Color.White	255,255,255
Color.black	0,0,0
Color.lightGray	192,192,192
Color.gray	128,128,128
Color.darkGray	64,64,64
Color.red	255,0,0
Color.green	0,255,0
Color.blue	0,0,255
Color.yellow	255,255,0
Color.magenta	255,0,255
Color.cyan	0,255,255
Color.pink	255,175,175
Color.orange	255,200,0

 

Testing and Setting the Current Colors

File name: ColorAppletDemo.java

import java.awt.*;

import java.awt.Font;

import java.applet.*;

/*

<applet code=ColorAppletDemo width=300 height=300>

</applet>

*/

public class ColorAppletDemo extends Applet{

public void paint(Graphics g){

Font f=new Font("TimesRoman",Font.BOLD,20);

Font f1=new Font("Courier",Font.ITALIC,20);

Font f2=new Font("Helevitica",Font.PLAIN,20);

g.setColor(Color.red);

g.setFont(f);

g.drawString("Be Happy.Be hopeful",30,30);

g.setColor(Color.blue);

g.setFont(f1);

g.drawString("Be happy.Be hopeful",30,70);

g.setColor(Color.pink);

g.setFont(f2);

g.drawString("Be happy.Be hopeful",30,110);

}

}

Output