Java Applets

In general, an applet is a small program or utility with limited features, requiring minimal resources, and usually designed to run within a larger program.

A Java applet is such a program written in the Java programming language and typically designed to run from a web browser.

Creating a Java Applet

1 . Write the applet in Java, and save it with a .java file extension, just as when you write a Java application.

2. Compile the applet into bytecode using the javac command, just as when you write a Java application.

3. Write an HTML document that includes a statement to call your compiled Java class.

4. Load the HTML document into a Web browser (such as Mozilla Firefox or Microsoft Internet Explorer), or open the HTML document using the Applet Viewer.

Creating HTML document

1. The tag that begins every HTML document is , which is surrounded by angle brackets.

2. The html within the tag is an HTML keyword that specifies that an HTML document follows the keyword.

3. The tag that ends every HTML document is .

Generally, HTML documents contain other tags with the texts. Of importance at this point is the tag pair used to run an applet from within an HTML document.

Three attributes (or arguments) are placed within the

Three attributes of the given object tag:

1. code = followed by the name of the compiled applet you are calling

2. width = followed by the width of the applet on the screen

3. height = followed by the height of the applet on the screen

Running an Applet

Two ways of running an applet:

1. by opening the associated HTML file on a Web browser

2. the appletviewer

Writing a Simple Applet

In creating an applet, you must also do the following:

1. Include import statements to ensure that necessary classes are available.

2. Learn to use some user interface (UI) components, such as buttons and text fields, and applet methods.

3. Learn to use the keyword extends.

Creators of Java created an applet class named JApplet that you can import using the statement,

import javax.swing.JApplet;


JApplet Class

JApplet is the Swing equivalent of the AWT Applet class.It is a simple extension of java.applet.Applet for use when creating Swing programs designed to be used in a Web browser.

As a direct subclass of Applet, JApplet is used in much the same way as the Applet.

A JApplet is a Component, and it is also a Container.

When using the JApplet class, you need the following import statements:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

The extends keyword indicates that your applet builds on, or inherits, the traits of the JApplet class.

Example 1:

//java file... save as .java file

import javax.swing.*;
import java.awt.*;

public class sampleApplet extends JApplet
{
public void init()
{
Container con = getContentPane();
cont.setLayout(new FlowLayout());
JLabel label = new JLabel("Hello world!");
con.add(label);
}
}

------------------------------
// html file... save as .html file



Output:
Example 2:

//java file... save as .java file

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class sampleAppletRRA extends JApplet implements ActionListener
{
Container con = getContentPane();
JLabel question = new JLabel("What’s your name?");
JTextField answer = new JTextField(10);
JButton press = new JButton("Press me");

public void init()
{
con.add(question);
con.add(answer);
con.add(press);
con.setLayout(new FlowLayout());
press.addActionListener(this);
}

public void actionPerformed(ActionEvent e)
{
String name = answer.getText();
JOptionPane.showMessageDialog(null, "You pressed the button, " + name);
}
}

------------------------------
//html file... save as .html file



Output:




Try to create an applet that will accept 2 integer numbers and display the sum.