Network Basics in Java Programming

🔹 What is Networking in Java?

Networking in Java allows programs to communicate with other programs over a network — typically over the Internet or a local network (LAN).

Java provides a rich set of APIs in the java.net package to support network communication.
You can build client-server applications, send/receive data, and handle protocols like TCP/IP and UDP.

🔹 Key Concepts of Networking in Java

1. IP Address and Port

IP Address: Unique address of a computer on the network.
Port: A numeric identifier for a specific process or service on the computer.

2. Protocols

TCP (Transmission Control Protocol): Reliable, connection-oriented communication.
UDP (User Datagram Protocol): Connectionless, faster but less reliable.

🔹 Java Networking Classes

Class	Purpose
`InetAddress`	Represents IP addresses
`Socket`	Client-side TCP socket
`ServerSocket`	Server-side TCP socket
`DatagramSocket`	UDP socket
`DatagramPacket`	Packet of data for UDP
`URL`	Represents a URL
`URLConnection`	Represents a communication link to a URL

🔹 Basic Networking Operations in Java

1. Using InetAddress

Represents an IP address.
Can get IP address from hostname or vice versa.

Example:

InetAddress address = InetAddress.getByName("www.google.com");
System.out.println("IP Address: " + address.getHostAddress());
System.out.println("Host Name: " + address.getHostName());

2. Creating a TCP Client (Using Socket)

Connects to a server at a given IP address and port.

Socket socket = new Socket("localhost", 5000);
// Use socket.getInputStream() and socket.getOutputStream() to communicate

3. Creating a TCP Server (Using ServerSocket)

Listens for client connections on a port.

ServerSocket server = new ServerSocket(5000);
Socket clientSocket = server.accept(); // wait for client connection
// Communicate using clientSocket.getInputStream() and getOutputStream()

4. UDP Communication (DatagramSocket and DatagramPacket)

UDP is connectionless and sends packets of data.

Example sending UDP packet:

DatagramSocket socket = new DatagramSocket();
byte[] buffer = "Hello UDP".getBytes();
InetAddress address = InetAddress.getByName("localhost");
DatagramPacket packet = new DatagramPacket(buffer, buffer.length, address, 5000);
socket.send(packet);
socket.close();

🔹 Example: Simple TCP Client-Server Communication

Server.java

ServerSocket server = new ServerSocket(5000);
Socket client = server.accept();
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
PrintWriter out = new PrintWriter(client.getOutputStream(), true);

String msg = in.readLine();
System.out.println("Received: " + msg);
out.println("Message received");

Client.java

Socket socket = new Socket("localhost", 5000);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

out.println("Hello Server");
String response = in.readLine();
System.out.println("Server says: " + response);

🔹 Summary Table

Topic	Details
Package	`java.net`
IP Address	Unique network address
Port	Endpoint number for communication
Protocols	TCP (connection-oriented), UDP (connectionless)
Main Classes	`InetAddress`, `Socket`, `ServerSocket`, `DatagramSocket`
TCP Communication	Reliable, socket-based
UDP Communication	Fast, packet-based

Overview of TCP/IP

🔹 What is TCP/IP?

TCP/IP stands for Transmission Control Protocol / Internet Protocol. It is a set of communication protocols used to interconnect network devices on the internet or private networks.

It defines how data should be packetized, addressed, transmitted, routed, and received.
TCP/IP is the foundation for the internet and most modern networks.

🔹 TCP/IP Model Layers

TCP/IP protocols are organized into four abstraction layers:

Layer	Function	Examples of Protocols
Application	High-level protocols for apps and services	HTTP, FTP, SMTP, DNS, SSH
Transport	Reliable or unreliable data transfer	TCP (reliable), UDP (unreliable)
Internet	Addressing and routing packets	IP (IPv4, IPv6), ICMP, ARP
Network Interface	Physical transmission of data	Ethernet, Wi-Fi, ARP

🔹 Key Protocols

1. IP (Internet Protocol)

Handles addressing and routing of packets across networks.
Responsible for delivering packets from source to destination based on IP addresses.
Versions: IPv4 (most common), IPv6 (newer, larger address space).

2. TCP (Transmission Control Protocol)

Provides reliable, connection-oriented communication.
Ensures data packets arrive in order and without errors.
Establishes a connection before sending data (3-way handshake).
Handles retransmission of lost packets.

3. UDP (User Datagram Protocol)

Connectionless and unreliable protocol.
Sends packets called datagrams without establishing a connection.
Used for applications needing speed over reliability (e.g., video streaming, gaming).

🔹 How TCP/IP Works

Data from an application is divided into smaller units called packets.
TCP ensures packets are numbered and checks for errors.
IP handles addressing and routing the packets to their destination.
At the destination, TCP reassembles packets into the original data.
If packets are lost or damaged, TCP retransmits them.

🔹 TCP/IP in Java

Java's java.net package provides classes like Socket, ServerSocket (for TCP), and DatagramSocket, DatagramPacket (for UDP).
Java developers use TCP/IP protocols to create client-server applications, web services, and network tools.

🔹 Summary Table

Protocol	Purpose	Connection	Reliability	Use Cases
TCP	Reliable data transfer	Connection-oriented	Reliable	Web browsing, email, file transfer
UDP	Fast, low-overhead transmission	Connectionless	Unreliable	Streaming, gaming, VoIP
IP	Routing and addressing packets	N/A	N/A	Underpins all internet communication

Socket Programming in Java:

🔹 What is Socket Programming?

Socket programming is a way to enable communication between two programs (usually client and server) over a network.

A socket is an endpoint for sending or receiving data across a network.
It provides a bidirectional communication channel between two processes, possibly on different machines.

🔹 How Socket Programming Works

The server creates a ServerSocket that listens on a specific port.
The client creates a Socket and connects to the server’s IP address and port.
Once connected, both client and server can send and receive data through input and output streams attached to the socket.
After communication, the sockets are closed.

🔹 Key Java Classes for Socket Programming

Class	Description
`ServerSocket`	Listens for incoming client connections on a port
`Socket`	Represents a client-side or accepted server-side socket connection
`InputStream` / `OutputStream`	Streams to read from/write to the socket
`BufferedReader` / `PrintWriter`	Convenient wrappers for reading/writing text

🔹 Basic Workflow for TCP Socket Programming

On the Server Side:

Create a ServerSocket bound to a port.
Wait for a client to connect by calling accept().
Use the returned Socket to communicate with the client.
Read and write data via input/output streams.
Close the socket after communication ends.

On the Client Side:

Create a Socket specifying server IP and port.
Use input/output streams to send/receive data.
Close the socket after communication ends.

🔹 Simple Java Example: TCP Server and Client

Server Code (Server.java)

import java.net.*;
import java.io.*;

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(1234);
        System.out.println("Server listening on port 1234...");

        Socket clientSocket = serverSocket.accept(); // Wait for client
        System.out.println("Client connected.");

        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);

        String message = in.readLine();
        System.out.println("Received from client: " + message);

        out.println("Hello from server!");

        clientSocket.close();
        serverSocket.close();
    }
}

Client Code (Client.java)

import java.net.*;
import java.io.*;

public class Client {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("localhost", 1234);
        System.out.println("Connected to server.");

        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        out.println("Hello Server!");
        String response = in.readLine();
        System.out.println("Server says: " + response);

        socket.close();
    }
}

🔹 Key Points to Remember

Sockets use ports to identify communication endpoints.
TCP sockets are connection-oriented, ensuring reliable communication.
Use input/output streams to read/write data over sockets.
Always close sockets to free resources.
Exception handling (try-catch) is essential for robust networking code.

🔹 When to Use Socket Programming?

Building client-server applications like chat servers, multiplayer games.
Communicating between distributed systems.
Creating custom protocols over TCP/UDP.
Implementing network tools and utilities.

Proxy Servers

🔹 What is a Proxy Server?

A proxy server acts as an intermediary between a client (like your computer or browser) and the internet (or another network service). When you send a request (e.g., visit a website), it first goes to the proxy server, which then forwards the request to the destination server on your behalf. The response returns back through the proxy to you.

🔹 How Does a Proxy Server Work?

Client sends a request to the proxy server instead of directly to the destination.
Proxy evaluates the request (e.g., for caching, filtering, or logging).
Proxy forwards the request to the destination server.
Destination server sends response back to the proxy.
Proxy sends the response back to the client.

🔹 Types of Proxy Servers

Type	Purpose/Use Case
Forward Proxy	Sits between client and internet; controls or filters client requests (e.g., for web filtering, security)
Reverse Proxy	Sits between internet and one or more web servers; distributes incoming traffic, provides load balancing, SSL termination
Transparent Proxy	Does not modify requests or responses; often used for caching or monitoring
Anonymous Proxy	Hides client’s IP address to provide privacy
Caching Proxy	Saves copies of frequently accessed resources to speed up responses
Open Proxy	Publicly accessible proxy servers (often unsafe)

🔹 Why Use a Proxy Server?

Privacy: Hide your IP address and location.
Security: Block malicious sites, filter content, prevent direct access.
Caching: Reduce bandwidth by serving cached content.
Load Balancing: Distribute requests among multiple servers (reverse proxy).
Access Control: Restrict access to certain websites or services.
Logging and Monitoring: Track user activity.

🔹 Proxy Servers in Java

Java programs can use proxy servers by configuring:

System properties for HTTP, HTTPS proxies:

System.setProperty("http.proxyHost", "proxy.example.com");
System.setProperty("http.proxyPort", "8080");

Use Proxy class in java.net package to programmatically use proxies for Socket or HttpURLConnection.

Example:

Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("proxy.example.com", 8080));
HttpURLConnection connection = (HttpURLConnection) new URL("http://example.com").openConnection(proxy);

🔹 Summary Table

Aspect	Details
What is Proxy?	Intermediary between client and server
Types	Forward, Reverse, Transparent, Anonymous
Benefits	Privacy, Security, Caching, Load balancing
Java Support	System properties, `Proxy` class

TCP/IP Sockets

🔹 What Are TCP/IP Sockets?

A socket is one endpoint of a two-way communication link between two programs running on a network.
TCP/IP sockets use the TCP/IP protocol suite to establish reliable, ordered, and error-checked communication between client and server applications.
TCP (Transmission Control Protocol) ensures a connection-oriented, reliable data transfer, while IP (Internet Protocol) handles addressing and routing.

🔹 Key Concepts of TCP/IP Sockets

Term	Explanation
Socket	Combination of IP address and port number identifying an endpoint
Port	Logical communication endpoint for a process on a machine
IP Address	Unique address for a device on the network
TCP	Provides reliable, connection-oriented communication

🔹 How TCP/IP Sockets Work

Server Side:
Creates a ServerSocket listening on a specific port.
Waits (blocks) for incoming client connection requests.
When a client connects, the server accepts the connection, creating a new Socket for communication.
Communicates with the client through input/output streams attached to the socket.
Client Side:
Creates a Socket and connects to the server's IP address and port.
Uses input/output streams to send and receive data.
Data Transmission:
Data is broken down into packets by TCP/IP and sent over the network.
TCP guarantees packets arrive in order, retransmitting lost packets if necessary.

🔹 TCP/IP Socket Communication Steps

Step	Description
1. Socket creation	Server creates `ServerSocket`; client creates `Socket`
2. Connection	Client connects; server accepts connection
3. Data Exchange	Both sides send/receive data via streams
4. Termination	Either side closes socket to end communication

🔹 Java Classes for TCP/IP Sockets

Class	Purpose
`ServerSocket`	Listens for and accepts incoming connections
`Socket`	Represents client connection to server
`InputStream`	To read data from socket
`OutputStream`	To write data to socket
`BufferedReader`/`PrintWriter`	Easier handling of text data

🔹 Simple Example (Summary)

Server creates ServerSocket on port 5000.
Client creates Socket to connect to server on port 5000.
Both communicate via streams.

🔹 Why Use TCP/IP Sockets?

To build networked applications like chat apps, games, file transfer tools.
Enables reliable, ordered communication over the internet.
Works across different devices and platforms as TCP/IP is universal.

Network Address (Net Address)

🔹 What is a Network Address (Net Address)?

A network address is an identifier used to uniquely locate a device (host) or network on a larger network, such as the Internet.

It tells where a device is located in the network hierarchy.
It enables routing of data packets from one device to another.

🔹 Types of Network Addresses

Type	Description	Examples
IP Address	Numeric label assigned to each device on a network	IPv4 (e.g., 192.168.1.1), IPv6 (e.g., 2001:0db8::1)
MAC Address	Unique hardware address of a network interface card	00:1A:2B:3C:4D:5E
Subnet Address	Represents a segment of a larger network	Derived from IP & subnet mask

🔹 Network Address in TCP/IP

IP Address is the primary network address in TCP/IP.
It consists of two parts:
Network portion: Identifies the specific network.
Host portion: Identifies the specific device on that network.
The division depends on the subnet mask.

🔹 Network Address in Java (`InetAddress`)

Java provides the class java.net.InetAddress to represent IP addresses.

Can represent both IPv4 and IPv6 addresses.
Used for hostname resolution and IP manipulation.

Key Methods:

InetAddress.getByName(String host): Resolves hostname to IP address.
InetAddress.getHostAddress(): Returns the IP address as a string.
InetAddress.getHostName(): Returns the hostname.

Example:

import java.net.*;

public class NetworkAddressExample {
    public static void main(String[] args) throws Exception {
        InetAddress address = InetAddress.getByName("www.google.com");
        System.out.println("Host Name: " + address.getHostName());
        System.out.println("IP Address: " + address.getHostAddress());
    }
}

🔹 Summary

Term	Meaning
Network Address	Identifier for locating devices or networks
IP Address	Main network address in TCP/IP
`InetAddress`	Java class representing network addresses

URL in Java and networking:

🔹 What is a URL?

URL stands for Uniform Resource Locator.

It is the address used to locate resources on the internet, such as web pages, images, files, etc.
A URL tells the browser or program where to find the resource and how to access it.

🔹 Structure of a URL

A typical URL looks like this:

protocol://hostname:port/path?query#fragment

Part	Description	Example
Protocol	The method used to access the resource	`http`, `https`, `ftp`
Hostname	The domain name or IP address of the server	`www.example.com`
Port	(Optional) Port number where the server listens	`80` (default for HTTP)
Path	The specific resource on the server	`/index.html`
Query	(Optional) Parameters passed to the resource	`?id=123&sort=asc`
Fragment	(Optional) Section within the resource	`#section2`

🔹 URL Example

https://www.example.com:443/products/item1.html?color=red#details

Protocol: https
Hostname: www.example.com
Port: 443 (default for HTTPS)
Path: /products/item1.html
Query: color=red
Fragment: details

🔹 URL in Java (`java.net.URL`)

Java provides the URL class to work with URLs programmatically.

Key Features:

Parse URL strings into components (protocol, host, port, path, etc.).
Open streams to read data from the URL.
Access URL components via getter methods.

Example:

import java.net.*;

public class URLExample {
    public static void main(String[] args) throws Exception {
        URL url = new URL("https://www.example.com:443/products/item1.html?color=red#details");

        System.out.println("Protocol: " + url.getProtocol());
        System.out.println("Host: " + url.getHost());
        System.out.println("Port: " + url.getPort());           // Returns -1 if default port
        System.out.println("Path: " + url.getPath());
        System.out.println("Query: " + url.getQuery());
        System.out.println("Ref: " + url.getRef());
    }
}

🔹 Summary

Term	Meaning
URL	Uniform Resource Locator, address of resource
Protocol	Access method (HTTP, HTTPS, FTP, etc.)
Hostname	Server address
Port	Network port
Path	Resource location on server
Query	Parameters passed to resource
Fragment	Specific section within resource

Datagrams

🔹 What Are Datagrams?

A datagram is a basic transfer unit associated with connectionless packet-switched networks.
It is a self-contained, independent packet of data that carries enough information for routing from source to destination without relying on earlier exchanges.
Unlike TCP (connection-oriented), datagrams use UDP (User Datagram Protocol), which is connectionless and unreliable (no guaranteed delivery or order).

🔹 Characteristics of Datagrams

Feature	Description
Connectionless	No formal connection established before sending data
Unreliable	Packets may be lost, duplicated, or arrive out of order
Small Size	Each datagram fits within a single packet (usually up to 65,535 bytes)
Independent	Each datagram is handled independently by the network

🔹 Datagram in Java (`java.net.DatagramPacket` and `DatagramSocket`)

Java provides classes to handle UDP datagram communication:

DatagramPacket: Represents a datagram packet (data + destination/source address).
DatagramSocket: Socket for sending and receiving datagram packets.

🔹 How Datagram Communication Works in Java

Sending Side

Create a DatagramPacket with data and destination IP & port.
Send the packet through a DatagramSocket.

Receiving Side

Create an empty DatagramPacket with a buffer.
Use DatagramSocket to receive incoming packets.
Extract data and sender information from the packet.

🔹 Simple Java Example: UDP Datagram Sender and Receiver

Datagram Sender (UDPClient.java)

import java.net.*;

public class UDPClient {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket();
        String message = "Hello UDP Server";
        byte[] buffer = message.getBytes();

        InetAddress address = InetAddress.getByName("localhost");
        DatagramPacket packet = new DatagramPacket(buffer, buffer.length, address, 9876);

        socket.send(packet);
        socket.close();
    }
}

Datagram Receiver (UDPServer.java)

import java.net.*;

public class UDPServer {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket(9876);
        byte[] buffer = new byte[1024];

        DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
        socket.receive(packet);

        String received = new String(packet.getData(), 0, packet.getLength());
        System.out.println("Received: " + received);

        socket.close();
    }
}

🔹 When to Use Datagrams?

Applications where speed is critical, and some data loss is acceptable.
Examples: Video streaming, VoIP, online gaming, DNS queries.
Situations where the overhead of establishing a connection is too high.

🔹 Summary Table

Aspect	Datagram (UDP)	TCP (Socket)
Connection	Connectionless	Connection-oriented
Reliability	Unreliable (no guarantee of delivery/order)	Reliable (guaranteed delivery/order)
Use Cases	Real-time apps (streaming, games)	File transfer, web browsing

Working with Windows using AWT Classes

🔹 What is AWT?

AWT (Abstract Window Toolkit) is Java’s original platform-independent windowing, graphics, and user-interface widget toolkit. It provides classes to create GUI components like windows, buttons, text fields, menus, etc.

🔹 Working with Windows in AWT

In AWT, a window is a top-level container that can hold GUI components. The main classes related to windows are:

Class	Description
`Frame`	A top-level window with a title bar and border
`Window`	A basic window with no borders or title bar
`Dialog`	A popup window for user interaction

🔹 Creating a Window Using AWT

Key Steps:

Create a Frame object: The main window.
Set size and layout: Define dimensions and layout manager.
Add components: Buttons, labels, text fields, etc.
Make the window visible.
Handle window events (like closing).

🔹 Example: Creating a Simple Window with AWT

import java.awt.*;
import java.awt.event.*;

public class SimpleAWTWindow {
    public static void main(String[] args) {
        // Step 1: Create a Frame
        Frame frame = new Frame("My AWT Window");

        // Step 2: Set size
        frame.setSize(400, 300);

        // Step 3: Add a simple component
        Label label = new Label("Welcome to AWT Window");
        frame.add(label);

        // Step 4: Set layout (optional)
        frame.setLayout(new FlowLayout());

        // Step 5: Make window visible
        frame.setVisible(true);

        // Step 6: Handle window closing event
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.out.println("Window is closing");
                frame.dispose(); // Close window
                System.exit(0);   // Exit program
            }
        });
    }
}

Class	Purpose
`Frame`	Main application window with borders/title
`Window`	Basic window without decorations
`Dialog`	Popup dialog window
`Canvas`	Area to draw graphics
`Panel`	Container to group components

🔹 Handling Window Events

Use WindowListener interface or WindowAdapter class to handle window events like minimize, maximize, close.
Commonly handled event: windowClosing to exit the app gracefully.

🔹 Summary

Step	Description
Create `Frame`	Window with title and border
Set size/layout	Define appearance
Add components	Add buttons, labels, etc.
Make visible	Show the window
Handle events	Manage user interactions (close)

AWT Controls

🔹 What are AWT Controls?

AWT Controls are the basic GUI components provided by the Abstract Window Toolkit (AWT) that allow user interaction in Java applications.

They include things like buttons, text fields, checkboxes, lists, and more.

🔹 Common AWT Controls

Control	Description
Button	A clickable button to trigger actions
Label	Displays a text string or image (non-editable)
TextField	Single-line text input field
TextArea	Multi-line text input area
Checkbox	A box that can be checked or unchecked (true/false)
CheckboxGroup	Group of checkboxes allowing only one selection (radio buttons)
Choice	Drop-down list allowing user to select one option
List	List box allowing single or multiple selection
ScrollBar	Scroll bar component for scrolling
Panel	Container to group multiple controls

🔹 Description of Some Key Controls

1. Button

Used to perform an action when clicked.
Example:

Button btn = new Button("Click Me");

2. Label

Used to display a text or image.
Not editable.
Example:

Label lbl = new Label("Username:");

3. TextField

Used for single-line input.
Can set maximum length.
Example:

TextField tf = new TextField(20);  // 20 columns wide

4. Checkbox

Represents a boolean option.
Example:

Checkbox cb = new Checkbox("Subscribe to newsletter");

5. Choice

Drop-down list for selecting one option.
Example:

Choice choice = new Choice();
choice.add("Option 1");
choice.add("Option 2");

6. List

Displays a list of items for selection.
Can allow single or multiple selections.
Example:

List list = new List(4, true);  // 4 visible rows, multiple select enabled
list.add("Java");
list.add("Python");

🔹 Example: Using AWT Controls in a Frame

import java.awt.*;
import java.awt.event.*;

public class AWTControlsExample {
    public static void main(String[] args) {
        Frame frame = new Frame("AWT Controls Demo");
        frame.setLayout(new FlowLayout());

        Label lbl = new Label("Enter Name:");
        TextField tf = new TextField(20);
        Button btn = new Button("Submit");
        Checkbox cb = new Checkbox("Subscribe");

        frame.add(lbl);
        frame.add(tf);
        frame.add(cb);
        frame.add(btn);

        frame.setSize(300, 150);
        frame.setVisible(true);

        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent we) {
                frame.dispose();
                System.exit(0);
            }
        });
    }
}

🔹 Summary

Control	Use Case
Button	Trigger actions on click
Label	Display text/images
TextField	Single-line user input
Checkbox	Boolean choice
Choice	Drop-down selection
List	Multiple/single selection list

Layout Managers and Menus in Java AWT:

🔹 Layout Managers in Java AWT

What are Layout Managers?

Layout managers control how components are arranged inside a container (like a Frame or Panel).
They help organize GUI components automatically, managing their size and position based on rules.
Using layout managers avoids manual positioning and resizing.

Common AWT Layout Managers

Layout Manager	Description	Usage Example
FlowLayout	Places components in a row, left to right, wraps to next line	Default for `Panel`
BorderLayout	Divides container into 5 regions: North, South, East, West, Center	Default for `Frame`
GridLayout	Arranges components in a grid of rows and columns, all equal size	Buttons in calculator-like layout
CardLayout	Stacks components like cards; only one visible at a time	Wizard steps UI

1. FlowLayout

Components flow left to right.
When no space, wraps to next line.

Frame f = new Frame();
f.setLayout(new FlowLayout());

2. BorderLayout

Divides space into five areas.
Add components to specific areas:

Frame f = new Frame();
f.setLayout(new BorderLayout());

f.add(new Button("North"), BorderLayout.NORTH);
f.add(new Button("Center"), BorderLayout.CENTER);

3. GridLayout

Components arranged in rows and columns.
Each cell same size.

Frame f = new Frame();
f.setLayout(new GridLayout(2, 3)); // 2 rows, 3 columns

4. CardLayout

Used to swap between different "cards" or panels.
Useful for wizard dialogs.

🔹 Menus in Java AWT

A menu provides a list of options or commands the user can select.
In AWT, menus appear typically on the top of a window (like File, Edit).

Class	Description
MenuBar	The bar that holds menus (usually at the top)
Menu	A pull-down menu (e.g., File menu)
MenuItem	An individual item in a menu
CheckboxMenuItem	A menu item with a checkbox

import java.awt.*;
import java.awt.event.*;

public class MenuExample {
    public static void main(String[] args) {
        Frame f = new Frame("Menu Demo");

        // Create MenuBar
        MenuBar menuBar = new MenuBar();

        // Create Menus
        Menu fileMenu = new Menu("File");
        Menu editMenu = new Menu("Edit");

        // Create MenuItems
        MenuItem newItem = new MenuItem("New");
        MenuItem openItem = new MenuItem("Open");
        MenuItem exitItem = new MenuItem("Exit");

        // Add MenuItems to File menu
        fileMenu.add(newItem);
        fileMenu.add(openItem);
        fileMenu.addSeparator();
        fileMenu.add(exitItem);

        // Add menus to MenuBar
        menuBar.add(fileMenu);
        menuBar.add(editMenu);

        // Set MenuBar to Frame
        f.setMenuBar(menuBar);

        // Handle Exit menu item action
        exitItem.addActionListener(e -> {
            f.dispose();
            System.exit(0);
        });

        f.setSize(400, 300);
        f.setVisible(true);
    }
}

🔹 Summary

Topic	Purpose
Layout Managers	Control positioning and resizing of GUI components
FlowLayout	Simple left-to-right flow layout
BorderLayout	5-region layout (North, South, East, West, Center)
GridLayout	Grid of equal-sized cells
Menus	Provide user options like File, Edit menus
MenuBar/Menu/MenuItem	Components to create menus and items

JDBC Connectivity

🔹 What is JDBC?

JDBC stands for Java Database Connectivity.
It is an API (Application Programming Interface) in Java that allows Java programs to connect and interact with databases.
JDBC provides methods to query and update data in a database.

🔹 Why Use JDBC?

To connect Java applications with databases (like MySQL, Oracle, PostgreSQL).
To perform database operations like SELECT, INSERT, UPDATE, DELETE.
To execute SQL statements from Java.

🔹 JDBC Architecture Overview

JDBC API: Java interface that application programs use.
JDBC Driver Manager: Manages different database drivers.
JDBC Drivers: Implement specific database protocols.

🔹 Steps for JDBC Connectivity

Load the JDBC Driver
Establish a Connection to the database
Create a Statement or PreparedStatement
Execute SQL queries or updates
Process the ResultSet (if any)
Close the connection

🔹 Key Interfaces and Classes

Interface/Class	Purpose
`DriverManager`	Manages JDBC drivers
`Connection`	Represents a connection to the database
`Statement`	Used to execute static SQL statements
`PreparedStatement`	Used to execute precompiled SQL statements with parameters
`ResultSet`	Represents the result set from a query

🔹 Example: Simple JDBC Program

import java.sql.*;

public class JDBCExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase"; // database URL
        String user = "root";                                  // database username
        String password = "password";                          // database password

        try {
            // Step 1: Load JDBC driver (optional for newer JDBC versions)
            Class.forName("com.mysql.cj.jdbc.Driver");

            // Step 2: Establish connection
            Connection conn = DriverManager.getConnection(url, user, password);

            // Step 3: Create statement
            Statement stmt = conn.createStatement();

            // Step 4: Execute query
            ResultSet rs = stmt.executeQuery("SELECT * FROM employees");

            // Step 5: Process results
            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                System.out.println("ID: " + id + ", Name: " + name);
            }

            // Step 6: Close connections
            rs.close();
            stmt.close();
            conn.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

🔹 Important Points

Loading Driver: Since JDBC 4.0, drivers are auto-registered if in classpath, so Class.forName may be optional.
Connection URL: Format depends on the database (MySQL, Oracle, etc.)
SQL Injection: Always prefer PreparedStatement to avoid SQL injection.
Exception Handling: Handle SQLException.

🔹 Summary

Step	Description
Load Driver	Register JDBC driver
Connect to Database	Get connection using URL and credentials
Create Statement	Prepare SQL commands
Execute Query/Update	Run SQL against DB
Process ResultSet	Read returned data
Close Resources	Release DB resources

Network Basics in Java Programming

🔹 What is Networking in Java?

🔹 Key Concepts of Networking in Java

1. IP Address and Port

2. Protocols

🔹 Java Networking Classes

🔹 Basic Networking Operations in Java

1. Using InetAddress

2. Creating a TCP Client (Using Socket)

3. Creating a TCP Server (Using ServerSocket)

4. UDP Communication (DatagramSocket and DatagramPacket)

🔹 Example: Simple TCP Client-Server Communication

🔹 Summary Table

Overview of TCP/IP

🔹 What is TCP/IP?

🔹 TCP/IP Model Layers

🔹 Key Protocols

1. IP (Internet Protocol)

2. TCP (Transmission Control Protocol)

3. UDP (User Datagram Protocol)

🔹 How TCP/IP Works

🔹 TCP/IP in Java

🔹 Summary Table

Socket Programming in Java:

🔹 What is Socket Programming?

🔹 How Socket Programming Works

🔹 Key Java Classes for Socket Programming

🔹 Basic Workflow for TCP Socket Programming

On the Server Side:

On the Client Side:

🔹 Simple Java Example: TCP Server and Client

Server Code (Server.java)

Client Code (Client.java)

🔹 Key Points to Remember

🔹 When to Use Socket Programming?

Proxy Servers

🔹 What is a Proxy Server?

🔹 How Does a Proxy Server Work?

🔹 Types of Proxy Servers

🔹 Why Use a Proxy Server?

🔹 Proxy Servers in Java

🔹 Summary Table

TCP/IP Sockets

🔹 What Are TCP/IP Sockets?

🔹 Key Concepts of TCP/IP Sockets

🔹 How TCP/IP Sockets Work

🔹 TCP/IP Socket Communication Steps

🔹 Java Classes for TCP/IP Sockets

🔹 Simple Example (Summary)

🔹 Why Use TCP/IP Sockets?

Network Address (Net Address)

🔹 What is a Network Address (Net Address)?

🔹 Types of Network Addresses

🔹 Network Address in TCP/IP

🔹 Network Address in Java (InetAddress)

Key Methods:

Example:

🔹 Summary

URL in Java and networking:

🔹 What is a URL?

🔹 Structure of a URL

🔹 URL Example

🔹 URL in Java (java.net.URL)

Key Features:

Example:

🔹 Summary

Datagrams

🔹 What Are Datagrams?

🔹 Characteristics of Datagrams

🔹 Datagram in Java (java.net.DatagramPacket and DatagramSocket)

🔹 How Datagram Communication Works in Java

Sending Side

Receiving Side

🔹 Simple Java Example: UDP Datagram Sender and Receiver

Datagram Sender (UDPClient.java)

Datagram Receiver (UDPServer.java)

🔹 When to Use Datagrams?

🔹 Summary Table

Working with Windows using AWT Classes

🔹 What is AWT?

🔹 Network Address in Java (`InetAddress`)

🔹 URL in Java (`java.net.URL`)

🔹 Datagram in Java (`java.net.DatagramPacket` and `DatagramSocket`)