Java Applet Tutorial: Learning the Basics

Posted On: Thu Jul 25 2024
Posted By: Khim Panthi

Namaste! If you’re a Nepali student interested in coding and web development, you’re in for a treat. Today, we’re exploring Java applets. Java applets are small applications that run in a web browser, and learning about them will give you a great foundation in Java programming. It’s like chatting over a cup of chiya, so let's dive in!

Why Learn Java Applets?

Java applets provide a unique way to create interactive web applications. Although not as common today, understanding applets is valuable because it teaches fundamental Java concepts and how Java interacts with web technologies. Plus, it can be a fun way to learn and practice Java programming.

Getting Started with Java Applets

Setting Up Your Environment

To get started, ensure you have the latest Java Development Kit (JDK) installed. You can download it from the official Oracle website. You’ll also need a text editor or an Integrated Development Environment (IDE) like IntelliJ IDEA or Eclipse.

Your First Java Applet

Let’s create a simple applet. Open your IDE and create a new Java project. Inside your project, create a new class called HelloApplet.

import java.applet.Applet;

import java.awt.Graphics;

public class HelloApplet extends Applet {

public void paint(Graphics g) {

g.drawString("Hello, Nepali Students!", 20, 20);

}

This simple code creates a basic applet that displays the text "Hello, Nepali Students!".

Running the Applet

To run the applet, you’ll need an HTML file that references it. Create a file named HelloApplet.html in the same directory.

<!DOCTYPE html>

<html>

<head>

<title>Hello Applet</title>

</head>

<body>

</applet>

</body>

</html>

Open this HTML file in a web browser that supports Java applets. Note that modern browsers have discontinued support for Java applets, so you might need to use an older browser or a special setup to run it.

Understanding Java Applet Components

The Applet Class

In Java, an applet is a subclass of the Applet class from the java.applet package. The Applet class provides methods that you can override to create your applet.

The Paint Method

The paint method is called when the applet needs to redraw its output. It takes a Graphics object as a parameter, which you use to draw text, shapes, and images on the applet.

Example: Interactive Applet

Let’s create an interactive applet that changes its message when you click a button.

import java.applet.Applet;

import java.awt.Graphics;

import java.awt.Button;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

public class InteractiveApplet extends Applet implements ActionListener {

String message = "Hello, Nepali Students!";

Button changeMessageButton;

public void init() {

changeMessageButton = new Button("Click Me!");

add(changeMessageButton);

changeMessageButton.addActionListener(this);

}

public void paint(Graphics g) {

g.drawString(message, 20, 20);

}

public void actionPerformed(ActionEvent e) {

message = "You clicked the button!";

repaint();

}

This code creates an applet with a button. When you click the button, the message changes.

Advanced Java Applet Features

Using Parameters

Applets can accept parameters from the HTML file, allowing you to customize their behavior.

import java.applet.Applet;

import java.awt.Graphics;

public class ParameterApplet extends Applet {

String message;

public void init() {

message = getParameter("message");

if (message == null) {

message = "Hello, World!";

}

public void paint(Graphics g) {

g.drawString(message, 20, 20);

}

In the HTML file, you can pass a parameter like this:

<!DOCTYPE html>

<html>

<head>

<title>Parameter Applet</title>

</head>

<body>

</applet>

</body>

</html>

Handling User Input

You can enhance your applets by handling user input, such as text fields and buttons.

import java.applet.Applet;

import java.awt.Graphics;

import java.awt.TextField;

import java.awt.Button;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

public class InputApplet extends Applet implements ActionListener {

TextField inputField;

Button submitButton;

String message = "";

public void init() {

inputField = new TextField(20);

submitButton = new Button("Submit");

add(inputField);

add(submitButton);

submitButton.addActionListener(this);

}

public void paint(Graphics g) {

g.drawString(message, 20, 50);

}

public void actionPerformed(ActionEvent e) {

message = "You entered: " + inputField.getText();

repaint();

}

This applet takes user input from a text field and displays it when the button is clicked.

FAQs

Q1: What is a Java applet?

A Java applet is a small application that runs in a web browser. It’s written in Java and can provide interactive features to web pages.

Q2: How do I run a Java applet?

You need an HTML file that references the applet's class file. Open the HTML file in a web browser that supports Java applets.

Q3: What are the main methods of the Applet class?

The main methods are init(), start(), stop(), destroy(), and paint(Graphics g). These methods control the applet's lifecycle and behavior.

Q4: Are Java applets still used today?

Java applets are not commonly used today due to security concerns and the discontinuation of support in modern browsers. However, learning applets can help you understand Java's capabilities and historical web technologies.

Q5: What can I do after learning Java applets?

After learning applets, you can move on to JavaFX or other modern Java frameworks for creating rich internet applications. Your understanding of Java will also help in building desktop applications, Android apps, and server-side applications.

Conclusion

Learning Java applets provides a solid foundation in Java programming and web development concepts. Although not as prevalent today, the skills you gain are transferable to modern technologies.

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