Applet
luckpiya
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23 slides
Mar 01, 2019
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About This Presentation
Applet and its life cycle method
Slide Content
JAVA APPLET By: PRIYANKA PRADHAN 1
Applet An applet is a Java program that runs in a Web browser. An applet can be a fully functional Java application because it has the entire Java API at its disposal. PRIYANKA PRADHAN 2
Differences between an applet and a standalone Java application. An applet is a Java class that extends the java.applet.Applet class. A main() method is not invoked on an applet, and an applet class will not define main(). Applets are designed to be embedded within an HTML page. When a user views an HTML page that contains an applet, the code for the applet is downloaded to the user's machine. A JVM is required to view an applet. The JVM can be either a plug-in of the Web browser or a separate runtime environment. The JVM on the user's machine creates an instance of the applet class and invokes various methods during the applet's lifetime. Applets have strict security rules that are enforced by the Web browser. PRIYANKA PRADHAN 3
Life Cycle of an Applet init − This method is intended for whatever initialization is needed for your applet. It is called after the param tags inside the applet tag have been processed. start − This method is automatically called after the browser calls the init method. It is also called whenever the user returns to the page containing the applet after having gone off to other pages. stop − This method is automatically called when the user moves off the page on which the applet sits. It can, therefore, be called repeatedly in the same applet. destroy − This method is only called when the browser shuts down normally. Because applets are meant to live on an HTML page, you should not normally leave resources behind after a user leaves the page that contains the applet. paint − Invoked immediately after the start() method, and also any time the applet needs to repaint itself in the browser. The paint() method is actually inherited from the java.awt. PRIYANKA PRADHAN 4
Lifecycle methods for Applet: public void init(): is used to initialized the Applet. It is invoked only once. public void start(): is invoked after the init() method or browser is maximized. It is used to start the Applet. public void stop(): is used to stop the Applet. It is invoked when Applet is stop or browser is minimized. public void destroy(): is used to destroy the Applet. It is invoked only once. PRIYANKA PRADHAN 5
java.awt.Component class The Component class provides 1 life cycle method of applet. public void paint(Graphics g): is used to paint the Applet. It provides Graphics class object that can be used for drawing oval, rectangle, arc etc. PRIYANKA PRADHAN 6
How to run an Applet? There are two ways to run an applet By html file. By appletViewer tool (for testing purpose). PRIYANKA PRADHAN 7
//First.java import java.applet.Applet ; import java.awt.Graphics ; public class First extends Applet{ public void paint(Graphics g){ g.drawString ("welcome",150,150); } } PRIYANKA PRADHAN 8
myapplet.html <html> <body> <applet code=" First.class " width="300" height="300"> </applet> </body> </html> PRIYANKA PRADHAN 9
Simple example of Applet by appletviewer tool: To execute the applet by appletviewer tool, create an applet that contains applet tag in comment and compile it. After that run it by: appletviewer First.java. Now Html file is not required but it is for testing purpose only. PRIYANKA PRADHAN 10
//First.java import java.applet.Applet ; import java.awt.Graphics ; public class First extends Applet{ public void paint(Graphics g){ g.drawString ("welcome to applet",150,150); } } /* <applet code=" First.class " width="300" height="300"> </applet> */ PRIYANKA PRADHAN 11
To execute the applet by appletviewer tool, write in command prompt: c:\> javac First.java c:\> appletviewer First.java PRIYANKA PRADHAN 12
Displaying Graphics in Applet java.awt.Graphics class provides many methods for graphics programming PRIYANKA PRADHAN 13
Commonly used methods of Graphics class: public abstract void drawString (String str , int x, int y): is used to draw the specified string. public void drawRect ( int x, int y, int width, int height): draws a rectangle with the specified width and height. public abstract void fillRect ( int x, int y, int width, int height): is used to fill rectangle with the default color and specified width and height. public abstract void drawOval ( int x, int y, int width, int height): is used to draw oval with the specified width and height. public abstract void fillOval ( int x, int y, int width, int height): is used to fill oval with the default color and specified width and height. public abstract void drawLine ( int x1, int y1, int x2, int y2): is used to draw line between the points(x1, y1) and (x2, y2). public abstract boolean drawImage (Image img , int x, int y, ImageObserver observer): is used draw the specified image. PRIYANKA PRADHAN 14
Example of Graphics in applet: import java.applet.Applet ; import java.awt.*; public class GraphicsDemo extends Applet{ public void paint(Graphics g){ g.setColor ( Color.red ); g.drawString ("Welcome",50, 50); g.drawLine (20,30,20,300); g.drawRect (70,100,30,30); g.fillRect (170,100,30,30); g.drawOval (70,200,30,30); g.setColor ( Color.pink ); g.fillOval (170,200,30,30); g.drawArc (90,150,30,30,30,270); g.fillArc (270,150,30,30,0,180); } } PRIYANKA PRADHAN 15
myapplet.html <html> <body> <applet code=" GraphicsDemo.class " width="300" height="300"> </applet> </body> </html> PRIYANKA PRADHAN 16
Displaying Image in Applet import java.awt.*; import java.applet .*; public class DisplayImage extends Applet { Image picture; public void init() { picture = getImage ( getDocumentBase (),"sonoo.jpg"); } public void paint(Graphics g) { g.drawImage (picture, 30,30, this ); } } PRIYANKA PRADHAN 17
myapplet.html <html> <body> <applet code=" DisplayImage.class " width="300" height="300"> </applet> </body> </html> PRIYANKA PRADHAN 18
EventHandling in Applet import java.applet .*; import java.awt.*; import java.awt.event .*; public class EventApplet extends Applet implements ActionListener { Button b; TextField tf ; public void init(){ tf = new TextField (); tf.setBounds (30,40,150,20); b= new Button("Click"); b.setBounds (80,150,60,50); add(b);add( tf ); b.addActionListener ( this ); setLayout ( null ); } public void actionPerformed ( ActionEvent e){ tf.setText ("Welcome"); } } PRIYANKA PRADHAN 19
myapplet.html <html> <body> <applet code=" EventApplet.class " width="300" height="300"> </applet> </body> </html> PRIYANKA PRADHAN 20
Parameter in Applet We can get any information from the HTML file as a parameter. For this purpose, Applet class provides a method named getParameter (). Syntax: public String getParameter (String parameterName ) PRIYANKA PRADHAN 21
import java.applet.Applet ; import java.awt.Graphics ; public class UseParam extends Applet{ public void paint(Graphics g){ String str = getParameter (" msg "); g.drawString (str,50, 50); } } PRIYANKA PRADHAN 22
myapplet.html <html> <body> <applet code=" UseParam.class " width="300" height="300"> < param name=" msg " value="Welcome to applet"> </applet> </body> </html> PRIYANKA PRADHAN 23
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