Applets are small java programs developed for internet applications. An applet located on a server can be downloaded via Internet and executed on a local computer (client), they can be run using appletviewer
command on any web browser that supports java. Like, any application program applet can perform arithmetic operations, display graphics, play sounds, accept user input, create animation and play interactive games. Java applets make a significant impact on World Wide Web.
Limitation of applet over application program
Disadvantages of using Applets:
For creating any applet, java.applet.Applet
class must be inherited. It provides 4 life cycle methods:
The Component class provides 1 life cycle method of applet.
//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); } }
//First.html <html> <body> <applet code="First.class" width="300" height="300"> </applet> </body> </html>
To Run program: type in command prompt: appletviewer First.html
java.awt.Graphics class provides many methods for graphics programming. Commonly used methods of Graphics class:
//GraphicsDemo.java 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); } }
//GraphicsDemo.html <html> <body> <applet code="GraphicsDemo.class" width="300" height="300"> </applet> </body> </html>
Applet is mostly used in games and animation. For this purpose image is required to be displayed. The java.awt.Graphics class provide a method drawImage() to display the image.
Example of 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); } } <html> <body> <applet code="DisplayImage.class" width="300" height="300"> </applet> </body> </html>
As we perform event handling in AWT or Swing, we can perform it in applet also. Let's see the simple example of event handling in applet that prints a message by click on the button.
Example of 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"); } } <html> <body> <applet code="EventApplet.class" width="300" height="300"> </applet> </body> </html>
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);
Example of using parameter in Applet:
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); } } <html> <body> <applet code="UseParam.class" width="300" height="300"> <param name="msg" value="Welcome to applet"> </applet> </body> </html>