COMP3114›Applets and Swing

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Applets and Swing

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📘 Java API: Applets and Swing

🔷 PART 1: APPLETS IN JAVA

🔹 1. Definition

An applet is a small Java program that runs inside a web browser or applet viewer.

👉 Used for:

Interactive web applications
Animations
Simple games

🔹 2. Key Features

Runs on client side
No main() method
Extends Applet class
Controlled by browser
Uses GUI (AWT)

🔹 3. Life Cycle of an Applet

Applet execution follows a sequence of methods:

📌 Life Cycle Methods

Method	Purpose
`init()`	Initialize applet
`start()`	Start or resume
`paint(Graphics g)`	Display output
`stop()`	Pause execution
`destroy()`	Cleanup

🔹 4. Applet Life Cycle Flow

✔ Step-by-step:

Browser loads applet → init()
Applet starts → start()
Output displayed → paint()
User leaves page → stop()
Applet removed → destroy()

🔹 5. Example of Applet

import java.applet.Applet;
import java.awt.Graphics;

public class MyApplet extends Applet {
    public void paint(Graphics g) {
        g.drawString("Hello Applet", 50, 50);
    }
}

🔹 6. HTML to Run Applet

<html>
<body>
<applet code="MyApplet.class" width="300" height="300"></applet>
</body>
</html>

🔹 7. Advantages of Applets

Platform independent
Easy to embed in web pages
Secure execution environment

🔹 8. Limitations (Important for Exams ⚠️)

Requires browser support (now mostly obsolete)
Slow performance
Security restrictions

🔹 9. Diagram Description

📊 Applet Life Cycle Diagram:

Flow arrows: init() → start() → paint() → stop() → destroy()

🔷 PART 2: SWING IN JAVA

🔹 1. Definition

Swing is a modern Java GUI toolkit used to create rich desktop applications.

👉 It is part of:

Java Foundation Classes

🔹 2. Key Features

Platform independent
Lightweight components
Rich set of controls
Customizable look and feel

🔹 3. Common Swing Components

Component	Description
`JFrame`	Main window
`JButton`	Button
`JLabel`	Text display
`JTextField`	Input field
`JCheckBox`	Selection
`JTextArea`	Multi-line text

🔹 4. Basic Swing Example

import javax.swing.*;

public class SwingDemo {
    public static void main(String[] args) {
        JFrame f = new JFrame("Swing Example");

        JButton b = new JButton("Click");
        b.setBounds(100, 100, 100, 40);

        f.add(b);
        f.setSize(300, 300);
        f.setLayout(null);
        f.setVisible(true);
    }
}

🔹 5. Swing vs AWT

Feature	AWT	Swing
Components	Heavyweight	Lightweight
Look	OS dependent	Customizable
Flexibility	Less	More

🔹 6. Event Handling in Swing

Swing uses same event handling model:

Add listener to component
Override event method

✔ Example:

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

public class ButtonClick {
    public static void main(String[] args) {
        JFrame f = new JFrame();
        JButton b = new JButton("Click");

        b.setBounds(100, 100, 100, 40);

        b.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                System.out.println("Clicked!");
            }
        });

        f.add(b);
        f.setSize(300, 300);
        f.setLayout(null);
        f.setVisible(true);
    }
}

🔹 7. Advanced Swing Concepts

📌 1. Layout Managers

FlowLayout
BorderLayout
GridLayout

📌 2. MVC Architecture

Swing loosely follows:

Model → Data
View → UI
Controller → Logic

📌 3. Event Dispatch Thread (EDT)

GUI must run on EDT
Avoid long operations on UI thread

🔹 8. Important Rules

Always use JFrame as main container
Add components using add()
Use layout managers properly
Handle events using listeners

🔷 9. Applet vs Swing

Feature	Applet	Swing
Type	Web-based	Desktop GUI
Execution	Browser	Standalone
Modern Use	Obsolete	Widely used
Components	AWT-based	Advanced

📝 Likely Exam Questions

Define applet and its life cycle.
Explain applet life cycle methods.
Write a simple applet program.
What are advantages and limitations of applets?
Define Swing and its features.
Difference between AWT and Swing.
Write a Swing program with button.
Explain event handling in Swing.
What is Event Dispatch Thread?
Compare Applet and Swing.

📌 Quick Revision Summary

🔹 Applets

Run in browser
No main()
Life cycle: init → start → paint → stop → destroy
Now mostly obsolete

🔹 Swing

Used for desktop GUI
Lightweight and flexible
Components like JFrame, JButton
Uses event handling

Previous topic 3

Advanced issues of GUI and event handling

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Network Programming Concepts: JDBC

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Method

Purpose

init()

Initialize applet

start()

Start or resume

paint(Graphics g)

Display output

stop()

Pause execution

destroy()

Cleanup

Component

Description

JFrame

Main window

JButton

Button

JLabel

Text display

JTextField

Input field

JCheckBox

Selection

JTextArea

Multi-line text

🔹 4. Basic Swing Example

import javax.swing.*; public class SwingDemo { public static void main(String[] args) { JFrame f = new JFrame("Swing Example"); JButton b = new JButton("Click"); b.setBounds(100, 100, 100, 40); f.add(b); f.setSize(300, 300); f.setLayout(null); f.setVisible(true); } }

Feature

AWT

Swing

Components

Heavyweight

Lightweight

Look

OS dependent

Customizable

Flexibility

Less

🔹 6. Event Handling in Swing

Swing uses same event handling model:

Add listener to component

Override event method

✔ Example:

import javax.swing.*; import java.awt.event.*; public class ButtonClick { public static void main(String[] args) { JFrame f = new JFrame(); JButton b = new JButton("Click"); b.setBounds(100, 100, 100, 40); b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { System.out.println("Clicked!"); } }); f.add(b); f.setSize(300, 300); f.setLayout(null); f.setVisible(true); } }

Feature

Applet

Swing

Type

Web-based

Desktop GUI

Execution

Browser

Standalone

Modern Use

Obsolete

Widely used

Components

AWT-based

Advanced

📝 Likely Exam Questions

Define applet and its life cycle.

Explain applet life cycle methods.

Write a simple applet program.

What are advantages and limitations of applets?

Define Swing and its features.

Difference between AWT and Swing.

Write a Swing program with button.

Explain event handling in Swing.

What is Event Dispatch Thread?

Compare Applet and Swing.