Sunday, January 8, 2012

Playing Audio:


An applet can play an audio file represented by the AudioClip interface in the java.applet package. The AudioClip interface has three methods, including:
  • public void play(): Plays the audio clip one time, from the beginning.
  • public void loop(): Causes the audio clip to replay continually.
  • public void stop(): Stops playing the audio clip.
To obtain an AudioClip object, you must invoke the getAudioClip() method of the Applet class. The getAudioClip() method returns immediately, whether or not the URL resolves to an actual audio file. The audio file is not downloaded until an attempt is made to play the audio clip.
Following is the example showing all the steps to play an audio:
import java.applet.*;
import java.awt.*;
import java.net.*;
public class AudioDemo extends Applet
{
   private AudioClip clip;
   private AppletContext context;
   public void init()
   {
      context = this.getAppletContext();
      String audioURL = this.getParameter("audio");
      if(audioURL == null)
      {
         audioURL = "default.au";
      }
      try
      {
         URL url = new URL(this.getDocumentBase(), audioURL);
         clip = context.getAudioClip(url);
      }catch(MalformedURLException e)
      {
         e.printStackTrace();
         context.showStatus("Could not load audio file!");
      }
   }
   public void start()
   {
      if(clip != null)
      {
         clip.loop();
      }
   }
   public void stop()
   {
      if(clip != null)
      {
         clip.stop();
      }
   }
}
Now let us call this applet as follows:
<html>
<title>The ImageDemo applet</title>
<hr>
<applet code="ImageDemo.class" width="0" height="0">
<param name="audio" value="test.wav">
</applet>
<hr>
</html>

Displaying Images:


An applet can display images of the format GIF, JPEG, BMP, and others. To display an image within the applet, you use the drawImage() method found in the java.awt.Graphics class.
Following is the example showing all the steps to show images:
import java.applet.*;
import java.awt.*;
import java.net.*;
public class ImageDemo extends Applet
{
  private Image image;
  private AppletContext context;
  public void init()
  {
      context = this.getAppletContext();
      String imageURL = this.getParameter("image");
      if(imageURL == null)
      {
         imageURL = "java.jpg";
      }
      try
      {
         URL url = new URL(this.getDocumentBase(), imageURL);
         image = context.getImage(url);
      }catch(MalformedURLException e)
      {
         e.printStackTrace();
         // Display in browser status bar
         context.showStatus("Could not load image!");
      }
   }
   public void paint(Graphics g)
   {
      context.showStatus("Displaying image");
      g.drawImage(image, 0, 0, 200, 84, null);
      g.drawString("www.javalicense.com", 35, 100);
   }  
}
Now let us call this applet as follows:
<html>
<title>The ImageDemo applet</title>
<hr>
<applet code="ImageDemo.class" width="300" height="200">
<param name="image" value="java.jpg">
</applet>
<hr>
</html>

Event Handling: Applet


import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
import java.applet.Applet;
import java.awt.Graphics;


public class ExampleEventHandling extends Applet 
    implements MouseListener {

    StringBuffer strBuffer;

    public void init() {
 addMouseListener(this);
 strBuffer = new StringBuffer();
        addItem("initializing the apple ");
    }

    public void start() {
        addItem("starting the applet ");
    }

    public void stop() {
        addItem("stopping the applet ");
    }

    public void destroy() {
        addItem("unloading the applet");
    }

    void addItem(String word) {
        System.out.println(word);
        strBuffer.append(word);
        repaint();
    }

    public void paint(Graphics g) {
 //Draw a Rectangle around the applet's display area.
        g.drawRect(0, 0, 
     getWidth() - 1,
     getHeight() - 1);

 //display the string inside the rectangle.
        g.drawString(strBuffer.toString(), 10, 20);
    }

   
    public void mouseEntered(MouseEvent event) {
    }
    public void mouseExited(MouseEvent event) {
    }
    public void mousePressed(MouseEvent event) {
    }
    public void mouseReleased(MouseEvent event) {
    }

    public void mouseClicked(MouseEvent event) {
 addItem("mouse clicked! ");
    }
}

Now let us call this applet as follows:
<html>
<title>Event Handling</title>
<hr>
<applet code="ExampleEventHandling.class" 
width="300" height="300">
</applet>
<hr>
</html>

Application Conversion to Applets:


It is easy to convert a graphical Java application (that is, an application that uses the AWT and that you can start with the java program launcher) into an applet that you can embed in a web page.
Here are the specific steps for converting an application to an applet.
  1. Make an HTML page with the appropriate tag to load the applet code.
  2. Supply a subclass of the JApplet class. Make this class public. Otherwise, the applet cannot be loaded.
  3. Eliminate the main method in the application. Do not construct a frame window for the application. Your application will be displayed inside the browser.
  4. Move any initialization code from the frame window constructor to the init method of the applet. You don't need to explicitly construct the applet object.the browser instantiates it for you and calls the init method.
  5. Remove the call to setSize; for applets, sizing is done with the width and height parameters in the HTML file.
  6. Remove the call to setDefaultCloseOperation. An applet cannot be closed; it terminates when the browser exits.
  7. If the application calls setTitle, eliminate the call to the method. Applets cannot have title bars. (You can, of course, title the web page itself, using the HTML title tag.)
  8. Don't call setVisible(true). The applet is displayed automatically.

The Applet CLASS:


Every applet is an extension of the java.applet.Applet class. The base Applet class provides methods that a derived Applet class may call to obtain information and services from the browser context.
These include methods that do the following:
  • Get applet parameters
  • Get the network location of the HTML file that contains the applet
  • Get the network location of the applet class directory
  • Print a status message in the browser
  • Fetch an image
  • Fetch an audio clip
  • Play an audio clip
  • Resize the applet
Additionally, the Applet class provides an interface by which the viewer or browser obtains information about the applet and controls the applet's execution. The viewer may:
  • request information about the author, version and copyright of the applet
  • request a description of the parameters the applet recognizes
  • initialize the applet
  • destroy the applet
  • start the applet's execution
  • stop the applet's execution

Life Cycle of an Applet:


Four methods in the Applet class give you the framework on which you build any serious 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.

Java - Applets Basics


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.
There are some important differences between an applet and a standalone Java application, including the following:
  • 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. The security of an applet is often referred to as sandbox security, comparing the applet to a child playing in a sandbox with various rules that must be followed.
  • Other classes that the applet needs can be downloaded in a single Java Archive (JAR) file.

How to find the most appropriate Keywords?

  🔍 Step 1: Understand Your Business and Audience Define your products, services, or content . Identify your target audien...