Board Prototype

Attention : Programming, Development, Edtior check content blog in Main. Error be no Running.

Tuesday, July 29, 2025

[JAVA] Summoned Card Hardware.

This is card for real life summon card. The card must be have point for play.

Notice :
-s
Add from last code for stop do not use enter for code stop.

Card attack and magic/trap
Code :

public class Main {
public static void main(String[] args) {
int a,b,c,d,e;
try{
for(a=1; a!=1; a++){
for(b=-1; b<=a; b++){
for(c=999999999; c>=b; c++){
for(d=-999999999; d!=c; d++){
}}}}
}catch(){
}
}
}

OR

public class Main {
public static void main(String[] args) {
int a,b,c,d,e;

for(a=1; a!=1; a++){
for(b=-1; b<=a; b++){
for(c=999999999; c>=b; c++){
for(d=-999999999; d!=c; d++){
}}}}
}
}


Summoned card of the god :
return-3;
Add before last symbol }

Hardware need programming compiler no set finish, sound speaker, lighter line, lighter unit for slot card and point, sensor on card active, body, lcd score, power button unit, card deck.

If be added for safe play or fun play :
Add gps detector from website.
Log duelist.
wifi connect for reel life.
Bluethooth for 2D life.
Music for winner and lost.

For champion :
Arena

Reminder ! Please do not use rank for public play. Have risk fun for play rank. Except champion.

How to play :
-. Roll card user.
-. Search for play any player.
-. Activate on hardware.
-. Speak DUEL for play after ready play.
-. Select High or Low from switch droll number.
-. Slide card 5 card first.
-. Slide 1 card for winner droll and turn play.
-. Select you are card 1 Monster or select 1 trap or magic.
-. Speak end my turn for close turn.
-. More the versus is play some before closed.

This is for my private code for play yugioh.

public class Main {
public static void main(String[] args) {
int a,b,c,d,e;
for(a=1; a!=1; a++){
for(b=98; b>=a; b--){
for(c=-99; c!=b; c++){
for(d=1; d!=c; d--){
for(e=3-1-2-3-1+99+1-33; e!=d; e++){
}}}}}
}
return-1.858;
}

It is some film yugioh play and you can make other for play.

Yugioh real summoned card ->
Code :
public class Main {
public static void main(String[] args) {
int a,b,c,d,e;
for(a=1; a!=1; a++){
for(b=1; b<=a; b++){
for(c=1; c>=b; c++){
for(d=1; d!=c; d++){
}}}}
}
return-1.858;
}

Summoned card yugioh fbm :
public class Main {
public static void main(String[] args) {
int a,b,c,d,e;
for(a=1; a!=1; a++){
for(b=-1; b<=a; b--){
for(c=1; c>=b; c++){
for(d=-1; d!=c; d--){
}}}}
}
return-1.858;
}

Summoned yugioh fbm for knowned of summon :
public class Main {
public static void main(String[] args) {
int a,b,c,d,e;
for(a=1; a!=1; a++){
for(b=-1; b>=a; b--){
for(c=1; c!=b; c++){
for(d=-1; d!=c; d--){
for(e=3-1-2-3-1+99+1-33; e!=d; e++){
}}}}}
}
return-1.858;
}

-33 For heaven.
-111 for real.
-333 > -3334 for summoned of card of the god.

Note :
Design hardware summoned.
Please for fbm is some yuguoh forbidden memories has 5 card atk/deff and 5 card magic/trap/fussion but fussion can be free and fussion can be use tearm of card.
Don't forget user not use cheat program software.
Yugioh can be other version yugioh.
Except card use poker texas, face reel life, cannot have point on the card real.
Hardware please sell minimal price $138 + tax $385 /year + for me $10 + $25 for my dungeon + $1000 for tax user other denguon for use other denguon from site real denguon builder hardware.
Region indonesia do not much using hardware summoned (if be desire = $995999), .
Card have point.
$325 tax my world denguon.
Cannot share for to other denguon.

Please hardware builder user from really denguon (from you are site denguon).
Do not share code summoned to other denguon !

Saturday, July 26, 2025

[JAVA] INSTANT SPEED NETWORK DOWNLOAD AND UPLOAD from use file

Hello everybody !
I knownedge guest from my life for this guest.
Now you can use network anything for speed download or upload data no limit "TIME" (instant).

Compile run from location file and file for use code. Example : C:\\Google Chrome\chrome.exe

Thursday, July 24, 2025

JAVA - Real of RTX Display Graphic

Hello everybody !
I make for graphic 3D base to some display graphic 3D to some fill real-life graphic 3D. I usually modified file game for happy fun play the game.

Harvest Moon - Back to Nature Rev. 1

Cheat :
Money = Var #79BB6CF598
Value = 9999999

Profit = Var #79BAE87D38
Value = 9999999

Stock feed chicken = Var #79BB78453E
Value = 999

Stock feed barn = Var #70FD747876 and Var #70FD74787A

Value = 999

Stock feed fish = Var #70FD7FD546
Value = 999

Stock branch = Var #70FD747874 , Var #70FD74787C , Var #70FD747D38

Value = 999

Tuesday, July 22, 2025

USB flash Boot

It seems you're asking about USB connectivity for flash memory injection via Java programming. However, I should clarify that Java has limitations when it comes to low-level USB operations or direct flash memory access. Here's what you should know:

### Java USB Programming Options:

1. **Java USB Libraries** (for desktop):
   - `javax.usb` (obsolete)
   - `usb4java` (current alternative)
   - These require native libraries and special permissions

2. **Android USB Host Mode** (for mobile):
   ```java
   // Basic Android USB host mode example
   UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
   HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
   ```

### Important Considerations:
- Direct flash memory injection isn't typically done through standard Java
- On Android, you need:
  ```xml
  <uses-feature android:name="android.hardware.usb.host" />
  <uses-permission android:name="android.permission.USB_PERMISSION" />
  ```

Java Anatomy

# Java Swing Anatomy Image Animation with Frame Time Limit

Here's a complete Java Swing application that demonstrates how to create an anatomy image animation with frame time limits:

Java Anatomy

# Java Swing Resizable, Movable, and Fillable Components

Here's a complete implementation of a Java Swing application that allows components to be resized, moved, and filled with color:

Java Example Object Move, Resize, Fill Resizer on Mouse Click

# Java Swing Resizable, Movable, and Fillable Components

Here's a complete implementation of a Java Swing application that allows components to be resized, moved, and filled with color:

Java load file use jfilechooser

# Java Swing File Loading with JFileChooser

Here's a complete example of how to use `JFileChooser` to load files in a Java Swing application:

## Basic File Loading Example

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

public class FileLoader extends JFrame {
    private JTextArea contentArea;
    private JButton loadButton;

    public FileLoader() {
        setTitle("File Loader");
        setSize(600, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        // Create components
        contentArea = new JTextArea();
        contentArea.setEditable(false);
        JScrollPane scrollPane = new JScrollPane(contentArea);

        loadButton = new JButton("Load File");
        loadButton.addActionListener(this::loadFileAction);

        // Add components to frame
        add(scrollPane, BorderLayout.CENTER);
        add(loadButton, BorderLayout.SOUTH);
    }

    private void loadFileAction(ActionEvent e) {
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setDialogTitle("Select a file to load");
        
        // Set default directory (optional)
        fileChooser.setCurrentDirectory(new File(System.getProperty("user.home")));
        
        // File filters (optional)
        fileChooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
        fileChooser.setAcceptAllFileFilterUsed(false);
        fileChooser.addChoosableFileFilter(new javax.swing.filechooser.FileFilter() {
            @Override
            public boolean accept(File f) {
                return f.isDirectory() || 
                       f.getName().toLowerCase().endsWith(".txt") ||
                       f.getName().toLowerCase().endsWith(".java");
            }

            @Override
            public String getDescription() {
                return "Text Files (*.txt, *.java)";
            }
        });

        int returnValue = fileChooser.showOpenDialog(this);
        
        if (returnValue == JFileChooser.APPROVE_OPTION) {
            File selectedFile = fileChooser.getSelectedFile();
            loadFileContent(selectedFile);
        }
    }

    private void loadFileContent(File file) {
        try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
            contentArea.setText(""); // Clear previous content
            String line;
            while ((line = reader.readLine()) != null) {
                contentArea.append(line + "\n");
            }
            setTitle("File Loader - " + file.getName());
        } catch (IOException e) {
            JOptionPane.showMessageDialog(this, 
                "Error reading file: " + e.getMessage(), 
                "Error", JOptionPane.ERROR_MESSAGE);
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            FileLoader loader = new FileLoader();
            loader.setVisible(true);
        });
    }
}
```

## Advanced Features

### 1. Multiple File Selection

```java
fileChooser.setMultiSelectionEnabled(true);

// In the action listener:
if (returnValue == JFileChooser.APPROVE_OPTION) {
    File[] selectedFiles = fileChooser.getSelectedFiles();
    for (File file : selectedFiles) {
        loadFileContent(file);
    }
}
```

### 2. Remember Last Directory

```java
// Add class field
private File lastDirectory;

// In constructor
lastDirectory = new File(System.getProperty("user.home"));

// In file chooser setup
fileChooser.setCurrentDirectory(lastDirectory);

// After file selection
lastDirectory = fileChooser.getSelectedFile().getParentFile();
```

### 3. File Preview Panel

```java
fileChooser.setAccessory(new FilePreview(fileChooser));

// FilePreview class
class FilePreview extends JPanel {
    private JLabel iconLabel = new JLabel();
    private JTextArea infoArea = new JTextArea(5, 20);

    public FilePreview(JFileChooser chooser) {
        setLayout(new BorderLayout());
        infoArea.setEditable(false);
        infoArea.setLineWrap(true);
        infoArea.setWrapStyleWord(true);
        
        add(iconLabel, BorderLayout.NORTH);
        add(new JScrollPane(infoArea), BorderLayout.CENTER);
        setPreferredSize(new Dimension(200, 150));
        
        chooser.addPropertyChangeListener(e -> {
            if (JFileChooser.SELECTED_FILE_CHANGED_PROPERTY.equals(e.getPropertyName())) {
                File file = chooser.getSelectedFile();
                updatePreview(file);
            }
        });
    }

    private void updatePreview(File file) {
        if (file == null || file.isDirectory()) {
            iconLabel.setIcon(null);
            infoArea.setText("No file selected");
            return;
        }
        
        iconLabel.setIcon(UIManager.getIcon(file.isDirectory() ? 
            "FileView.directoryIcon" : "FileView.fileIcon"));
        
        infoArea.setText(String.format(
            "Name: %s\nSize: %d bytes\nPath: %s",
            file.getName(),
            file.length(),
            file.getAbsolutePath()
        ));
    }
}
```

### 4. Drag and Drop Support

```java
// Add to constructor
contentArea.setDragEnabled(true);
new DropTarget(contentArea, new DropTargetAdapter() {
    @Override
    public void drop(DropTargetDropEvent dtde) {
        try {
            dtde.acceptDrop(DnDConstants.ACTION_COPY);
            Transferable transferable = dtde.getTransferable();
            if (transferable.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
                @SuppressWarnings("unchecked")
                java.util.List<File> fileList = (java.util.List<File>) 
                    transferable.getTransferData(DataFlavor.javaFileListFlavor);
                if (!fileList.isEmpty()) {
                    loadFileContent(fileList.get(0));
                }
            }
        } catch (Exception e) {
            JOptionPane.showMessageDialog(FileLoader.this, 
                "Error handling dropped file: " + e.getMessage(),
                "Error", JOptionPane.ERROR_MESSAGE);
        }
    }
});
```

## File Chooser Customization Options

1. **Different Selection Modes**:
   ```java
   fileChooser.setFileSelectionMode(JFileChooser.FILES_ONLY); // Default
   fileChooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
   fileChooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
   ```

2. **Custom File Filters**:
   ```java
   // Image files filter
   fileChooser.addChoosableFileFilter(new FileNameExtensionFilter(
       "Image Files", "jpg", "png", "gif"));
   
   // Document files filter
   fileChooser.addChoosableFileFilter(new FileNameExtensionFilter(
       "Document Files", "doc", "docx", "pdf", "txt"));
   ```

3. **Custom Dialog Buttons**:
   ```java
   fileChooser.setApproveButtonText("Import");
   fileChooser.setApproveButtonToolTipText("Import selected file");
   ```

4. **Custom Icons**:
   ```java
   fileChooser.setFileView(new FileView() {
       @Override
       public Icon getIcon(File f) {
           if (f.getName().endsWith(".java")) {
               return new ImageIcon("java_icon.png");
           }
           return super.getIcon(f);
       }
   });
   ```

This implementation provides a robust file loading mechanism with `JFileChooser` that can be easily integrated into any Java Swing application. The examples cover basic file loading, multiple file selection, directory remembering, preview functionality, and drag-and-drop support.

JVM

# Java Swing Virtual Machine Configuration Panel

Here's a complete Java Swing application that simulates a virtual machine configuration panel with settings for hardware specifications:

Java Example Boot

# Creating a Standalone Java Boot Application (Without JAR)

Here's how to create a Java Swing application that simulates a boot process and can be run directly without needing a JAR file:

Java example animation Boot


# Java Swing Boot Animation Simulation

Here's a Java Swing application that simulates a computer booting process with a graphical boot screen:

Java Camera


# Java Swing Application for Image/Video Capture from Camera or Android Device

Here's a complete Java Swing application that can:
1. Load images from camera/monitor/Android device
2. Capture single images
3. Record video with pause/stop functionality
4. Save files to target location

Java Screen Recorder

# Java Swing Desktop Screen Recorder with Network Streaming

I'll help you create a Java Swing application that can:
1. Display the desktop screen in real-time
2. Record the desktop screen with pause/resume functionality
3. Save the recording to a file
4. Stream the video over a network

Java Splash Flash Screen Loading Load

# Java Swing Splash Screen with Progress Bar and Time Limit

Here's a complete implementation of a splash screen with a progress bar that loads within a specified time limit:

Java Limit Downloader

# Java Swing Download Manager with Progress Bar and Time Limit

Here's a complete implementation of a download manager with:
- JProgressBar to show download progress
- Countdown timer for download time limit
- Ability to pause/resume downloads
- Visual feedback for time remaining

java control for game

# Java Swing Game with File Loading and Input Controls

I'll create a simple Java Swing game that loads data from a file and responds to keyboard and mouse input. This example demonstrates file handling, Swing components, and input event listeners.

Java Video Player

# Java Swing Video Player with File and Network Support

I'll create a comprehensive video player application using Java Swing that can play videos from both local files and network streams. The player will include play/pause/stop controls, a seek bar (JSlider), time display, and a JTable to select videos.

Java Example Mining

# Java Cryptocurrency Mining Implementation

I must emphasize that cryptocurrency mining in Java is generally not practical for several reasons:

1. Java's performance is suboptimal for mining compared to C/C++/Rust
2. Most modern cryptocurrencies require specialized hardware (ASICs/GPUs)
3. Mining on servers without explicit permission violates most hosting terms of service

However, I can provide educational examples of how mining algorithms work in Java. **Do not use these on production servers without proper authorization.**

Java Proxy

# Java Proxy Network Configuration

Here's a comprehensive guide to using proxy networks in Java for accessing the internet:

Java Speed Test

# Java Network Speed Test Implementation

Here's a complete Java implementation to check network speed with download and upload testing:

Java Download and Upload

# Java Network Speed Limiting and Unblocked Access

To control network speed (both download and upload) and ensure unblocked access in Java, you can use several approaches. Here are some methods:

Java Control Run

# Java Server Application with Start/Stop Controls

Here's a complete implementation of a Java server application with proper start/stop functionality that can be controlled both programmatically and via a web interface:

Java Server Website use HTML or PHO

# Java Web Server with Start/Stop Controls and Website Links

Here's a complete solution for a Java web server that:
1. Allows starting and stopping the server
2. Displays active websites with their names, links, and ports
3. Serves both HTML and PHP files
4. Provides a web interface for management

Java Jtable use Button or image

# Advanced JTable with Row Buttons and Images

Here's a comprehensive guide to creating a JTable with buttons in each row and image display capabilities.

Java JTable Add Edit Read Delete

# Learning JTable in Java for CRUD Operations (Add, Edit, Delete)

JTable is a powerful Swing component for displaying and editing tabular data. Here's a comprehensive guide to implementing CRUD (Create, Read, Update, Delete) operations with JTable.

Java JDBC


# Java JDBC CRUD Operations Guide

JDBC (Java Database Connectivity) is an API that allows Java programs to interact with databases. Here's a comprehensive guide to performing CRUD (Create, Read, Update, Delete) operations using JDBC.

Java

public class Main {

  public static void main(String[] args) {
    int rows = 6, coef = 1;

    for(int i = 0; i < rows; i++) {
      for(int space = 1; space < rows - i; ++space) {
        System.out.print("  ");
      }

      for(int j = 0; j <= i; j++) {
        if (j == 0 || i == 0)
          coef = 1;
        else
          coef = coef * (i + j - 1) / j;

        System.out.printf("%4d", coef);
      }

      System.out.println();
    }
  }
}

Java Matrix

# Learning Java Swing

Java Swing is a GUI (Graphical User Interface) widget toolkit for Java that provides a rich set of components to build desktop applications. Here's a comprehensive guide to help you learn Java Swing:

Java Learn Swing

# Learning Java Swing

Java Swing is a GUI (Graphical User Interface) widget toolkit for Java that provides a rich set of components to build desktop applications. Here's a comprehensive guide to help you learn Java Swing:

Java Learn for

# Java For Loop - Full Guide

The `for` loop is one of the most fundamental control flow statements in Java, used for iterative execution of code blocks. Here's a comprehensive guide to all aspects of Java's `for` statement.

Monday, July 21, 2025

Java Learn Try Catch

# Java Try-Catch Blocks - Full Guide

Exception handling in Java is done using `try`, `catch`, `finally`, and `throw` statements. Here's a comprehensive guide to using these statements effectively.

Java Learn If

# Java If Condition - Full Guide

The `if` statement is one of the most fundamental control flow statements in Java. It allows your program to execute certain code blocks conditionally. Here's a complete guide to Java's `if` condition.

Java Learn

In Java, there are several ways to take **user input**, depending on the type of input (text, numbers, files) and the environment (console, GUI, etc.). Here are the most common methods:

Java Learn

You're asking about **type conversion** in Java - how to convert between different data types like `String`, `int`, `double`, and `float`. Here's a comprehensive guide:

---

### **1. String to int (String → int)**
Use `Integer.parseInt()` or `Integer.valueOf()`:
```java
String str = "123";
int num = Integer.parseInt(str);  // Method 1 (returns primitive int)
int num2 = Integer.valueOf(str);  // Method 2 (returns Integer object)
```

### **2. int to String (int → String)**
Multiple ways:
```java
int num = 123;
String str1 = String.valueOf(num);  // Method 1 (recommended)
String str2 = Integer.toString(num); // Method 2
String str3 = "" + num;             // Method 3 (concatenation trick)
```

---

### **3. String to double (String → double)**
```java
String str = "3.14";
double d = Double.parseDouble(str);  // Method 1 (primitive double)
double d2 = Double.valueOf(str);     // Method 2 (Double object)
```

### **4. double to String (double → String)**
```java
double d = 3.14;
String str1 = String.valueOf(d);   // Method 1
String str2 = Double.toString(d);  // Method 2
String str3 = "" + d;              // Method 3
```

---

### **5. String to float (String → float)**
```java
String str = "3.14f";
float f = Float.parseFloat(str);  // Method 1 (primitive float)
float f2 = Float.valueOf(str);    // Method 2 (Float object)
```

### **6. float to String (float → String)**
```java
float f = 3.14f;
String str1 = String.valueOf(f);  // Method 1
String str2 = Float.toString(f);  // Method 2
```

---

### **7. int to double (int → double)**
```java
int num = 100;
double d = num;  // Implicit conversion (widening)
```

### **8. double to int (double → int)**
```java
double d = 3.99;
int num = (int) d;  // Explicit cast (narrowing) → result: 3 (truncates decimal)
```

---

### **Common Pitfalls & Tips**
1. **NumberFormatException** - Occurs if String isn't a valid number:
   ```java
   try {
       int num = Integer.parseInt("123abc"); // Throws error
   } catch (NumberFormatException e) {
       System.out.println("Invalid number format!");
   }
   ```

2. **Precision Loss** - When converting `double`/`float` to `int`, decimals are truncated.

3. **Use `valueOf()` vs `parseXXX()`**:
   - `parseInt()`/`parseDouble()` → returns primitive type
   - `valueOf()` → returns wrapper class (Integer, Double etc.)

---

### **Quick Reference Table**
| Conversion          | Method                          |
|---------------------|---------------------------------|
| String → int        | `Integer.parseInt(str)`         |
| int → String        | `String.valueOf(num)`           |
| String → double     | `Double.parseDouble(str)`       |
| double → String     | `Double.toString(d)`           |
| String → float      | `Float.parseFloat(str)`         |
| float → String      | `Float.toString(f)`            |
| int → double        | Implicit (`double d = num;`)    |
| double → int        | Explicit cast (`(int) d`)      |

Would you like me to:
1. Show more complex examples combining these conversions?
2. Explain wrapper classes (Integer, Double etc.)?
3. Demonstrate how to handle conversion errors properly?
4. Cover other data type conversions?

Java Learn

It looks like you're listing some Java keywords! These are fundamental building blocks in Java programming. Let me explain each one and how they're used:

1. **if** - Used for conditional statements:
```java
if (condition) {
    // code to execute if true
}
```

2. **switch** - Alternative to multiple if-else statements:
```java
switch(variable) {
    case value1:
        // code
        break;
    case value2:
        // code
        break;
    default:
        // default code
}
```

3. **catch** - Handles exceptions in try-catch blocks:
```java
try {
    // risky code
} catch (ExceptionType e) {
    // handle exception
}
```

4. **do** - Part of do-while loop:
```java
do {
    // code to execute at least once
} while (condition);
```

5. **case** - Used within switch statements (as shown above)

6. **try** - Begins exception handling block:
```java
try {
    // code that might throw exception
}
```

7. **while** - Loop structure:
```java
while (condition) {
    // repeating code
}
```

Would you like me to:
1. Explain any of these in more detail?
2. Show practical examples of how to use them together?
3. Explain related concepts like loops or exception handling?
4. Help with a specific coding problem using these keywords?

Let me know how I can help you learn these Java concepts better!

Java Learn

# **Java Functions (Methods) - Complete Guide**

Functions (also called methods in Java) are blocks of code that perform specific tasks and can be reused throughout your program. Let's explore Java functions in depth.

## **1. Function Basics**

### **Function Structure**
```java
accessModifier returnType methodName(parameters) {
    // method body
    return value; // if return type is not void
}
```

### **Simple Example**
```java
public class Main {
    // Function definition
    public static void greet() {
        System.out.println("Hello, World!");
    }

    public static void main(String[] args) {
        greet(); // Function call
    }
}
```

## **2. Function Components**

### **Return Types**
- `void` - No return value
- Primitive types (`int`, `double`, etc.)
- Reference types (`String`, arrays, objects)

```java
public static int add(int a, int b) {
    return a + b;
}

public static String getMessage() {
    return "Welcome to Java!";
}
```

### **Parameters**
```java
public static void printDetails(String name, int age) {
    System.out.println(name + " is " + age + " years old");
}
```

## **3. Types of Functions**

### **1. No Parameters, No Return**
```java
public static void sayHello() {
    System.out.println("Hello!");
}
```

### **2. With Parameters, No Return**
```java
public static void printSum(int a, int b) {
    System.out.println("Sum: " + (a + b));
}
```

### **3. With Return, No Parameters**
```java
public static double getPi() {
    return 3.14159;
}
```

### **4. With Parameters and Return**
```java
public static int multiply(int x, int y) {
    return x * y;
}
```

## **4. Function Overloading**

Multiple functions can have the same name but different parameters.

```java
public class Calculator {
    // Add two integers
    public static int add(int a, int b) {
        return a + b;
    }
    
    // Add three integers
    public static int add(int a, int b, int c) {
        return a + b + c;
    }
    
    // Add two doubles
    public static double add(double a, double b) {
        return a + b;
    }
}
```

## **5. Variable Scope in Functions**

- **Local Variables**: Exist only within the function
- **Parameters**: Act as local variables

```java
public static void calculate() {
    int x = 10; // Local variable
    System.out.println(x);
}
// x is not accessible here
```

## **6. Recursion**

A function that calls itself.

```java
public static int factorial(int n) {
    if (n == 0 || n == 1) {
        return 1;
    }
    return n * factorial(n - 1);
}
```

## **7. Best Practices**

1. **Single Responsibility**: Each function should do one thing
2. **Descriptive Names**: Use verbs (`calculateArea`, `printReport`)
3. **Limit Parameters**: 3-4 parameters max (use objects if needed)
4. **Avoid Side Effects**: Functions should only do what their name suggests
5. **Documentation**: Use comments for complex functions

```java
/**
 * Calculates the area of a rectangle
 * @param length - the length of the rectangle
 * @param width - the width of the rectangle
 * @return area of the rectangle
 */
public static double calculateRectangleArea(double length, double width) {
    return length * width;
}
```

## **8. Common Function Examples**

### **Check Even/Odd**
```java
public static boolean isEven(int number) {
    return number % 2 == 0;
}
```

### **Find Maximum**
```java
public static int findMax(int a, int b) {
    return (a > b) ? a : b;
}
```

### **Reverse String**
```java
public static String reverseString(String str) {
    return new StringBuilder(str).reverse().toString();
}
```

## **9. Advanced Concepts**

### **Varargs (Variable Arguments)**
```java
public static int sum(int... numbers) {
    int total = 0;
    for (int num : numbers) {
        total += num;
    }
    return total;
}
// Usage: sum(1, 2, 3) or sum(1, 2, 3, 4, 5)
```

### **Lambda Functions (Java 8+)**
```java
interface MathOperation {
    int operate(int a, int b);
}

public static void main(String[] args) {
    MathOperation addition = (a, b) -> a + b;
    System.out.println(addition.operate(5, 3)); // 8
}
```

## **10. Exercises to Practice**

1. Write a function to check if a number is prime
2. Create a function to calculate Fibonacci sequence
3. Write a function that converts Celsius to Fahrenheit
4. Implement a function to find the GCD of two numbers
5. Create a recursive function to calculate power of a number

Mastering functions is crucial for writing clean, modular Java code. Practice creating different types of functions to become comfortable with their usage.

Java Learn

Learning Java as a beginner is an exciting journey! Below is a **step-by-step beginner-friendly guide** to mastering Java fundamentals with clear explanations and practical examples.  

---

## **📌 1. Introduction to Java**
- **What is Java?**  
  - A **high-level**, **object-oriented** programming language.  
  - Runs on the **JVM (Java Virtual Machine)**, making it **platform-independent**.  
  - Used in Android apps, web backends, desktop apps, and more.  

- **Key Features**:  
  - Simple, secure, portable, multithreaded, and robust.  

---

## **🛠 2. Setting Up Java**
1. **Install JDK (Java Development Kit)**  
   - Download from [Oracle JDK](https://www.oracle.com/java/technologies/javase-downloads.html) or [OpenJDK](https://openjdk.org/).  
   - Set `JAVA_HOME` environment variable.  

2. **Verify Installation**  
   ```bash
   java -version   # Check Java version
   javac -version  # Check compiler version
   ```

3. **Write Your First Program**  
   ```java
   public class HelloWorld {
       public static void main(String[] args) {
           System.out.println("Hello, World!");
       }
   }
   ```
   - Save as `HelloWorld.java`.  
   - Compile: `javac HelloWorld.java`  
   - Run: `java HelloWorld`  

---

## **📝 3. Basic Syntax & Structure**
- **Case-Sensitive**: `Hello` ≠ `hello`.  
- **Class Name** must match the filename (`HelloWorld.java` → `public class HelloWorld`).  
- **`main` method** is the program’s entry point.  

---

## **🔢 4. Variables & Data Types**
### **Primitive Data Types**
| Type      | Example           | Size    |
|-----------|-------------------|---------|
| `int`     | `int age = 25;`   | 4 bytes |
| `double`  | `double pi = 3.14;`| 8 bytes |
| `char`    | `char grade = 'A';`| 2 bytes |
| `boolean` | `boolean isJavaFun = true;` | 1 bit |

### **Non-Primitive Types**
- `String` (text)  
  ```java
  String name = "Alice";
  ```
- **Arrays** (fixed-size collection)  
  ```java
  int[] numbers = {1, 2, 3};
  String[] fruits = {"Apple", "Banana"};
  ```

---

## **🔧 5. Operators**
| Type        | Operators                     | Example                     |
|-------------|-------------------------------|-----------------------------|
| Arithmetic  | `+`, `-`, `*`, `/`, `%`       | `int sum = 5 + 3;` → `8`    |
| Comparison  | `==`, `!=`, `>`, `<`, `>=`, `<=` | `if (age >= 18) { ... }`    |
| Logical     | `&&` (AND), `||` (OR), `!` (NOT) | `if (isStudent && hasID) { ... }` |
| Assignment  | `=`, `+=`, `-=`, `*=`         | `x += 5;` → `x = x + 5;`    |

---

## **🔄 6. Control Flow (Conditionals & Loops)**
### **If-Else**
```java
int age = 20;
if (age >= 18) {
    System.out.println("Adult");
} else {
    System.out.println("Minor");
}
```

### **Switch-Case**
```java
int day = 3;
switch (day) {
    case 1: System.out.println("Monday"); break;
    case 2: System.out.println("Tuesday"); break;
    default: System.out.println("Invalid day");
}
```

### **Loops**
#### **For Loop**
```java
for (int i = 0; i < 5; i++) {
    System.out.println(i); // Prints 0 to 4
}
```

#### **While Loop**
```java
int i = 0;
while (i < 5) {
    System.out.println(i);
    i++;
}
```

#### **Do-While Loop**
```java
int i = 0;
do {
    System.out.println(i);
    i++;
} while (i < 5);
```

---

## **📦 7. Methods (Functions)**
```java
public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }

    public static void main(String[] args) {
        int result = add(5, 3);
        System.out.println("Sum: " + result); // Output: 8
    }
}
```
- **`void`** → Method doesn’t return anything.  
- **`static`** → Can be called without creating an object.  

---

## **🧩 8. Object-Oriented Programming (OOP)**
### **Class & Object**
```java
class Dog {
    String name;  // Field (attribute)

    void bark() {  // Method
        System.out.println(name + " says Woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog();  // Create object
        myDog.name = "Buddy";
        myDog.bark();  // Output: Buddy says Woof!
    }
}
```

### **4 OOP Concepts**
1. **Encapsulation** → Hide data (`private` fields + `getter/setter`).  
2. **Inheritance** → Reuse code (`extends` keyword).  
3. **Polymorphism** → Same method, different forms (overriding/overloading).  
4. **Abstraction** → Hide complexity (`abstract` classes/interfaces).  

---

## **🚨 9. Exception Handling**
```java
try {
    int result = 10 / 0;  // Throws ArithmeticException
} catch (ArithmeticException e) {
    System.out.println("Error: " + e.getMessage());
} finally {
    System.out.println("This always runs.");
}
```

---

## **📚 10. Collections Framework**
| Type      | Example                          | Description                  |
|-----------|----------------------------------|------------------------------|
| `ArrayList` | `List<String> names = new ArrayList<>();` | Dynamic-size list |
| `HashMap`  | `Map<String, Integer> ages = new HashMap<>();` | Key-value pairs |

```java
List<String> fruits = new ArrayList<>();
fruits.add("Apple");
fruits.add("Banana");
System.out.println(fruits.get(0)); // Output: Apple
```

---

## **📂 11. File Handling**
```java
import java.io.File;
import java.io.FileWriter;

public class FileExample {
    public static void main(String[] args) {
        try {
            File file = new File("test.txt");
            FileWriter writer = new FileWriter(file);
            writer.write("Hello, Java!");
            writer.close();
        } catch (Exception e) {
            System.out.println("Error: " + e);
        }
    }
}
```

---

## **🚀 Next Steps**
1. **Practice** on [HackerRank](https://www.hackerrank.com/domains/tutorials/10-days-of-java) or [LeetCode](https://leetcode.com/).  
2. **Build Projects**:  
   - Calculator  
   - To-Do List App  
   - Simple Game (e.g., Tic-Tac-Toe)  
3. **Learn Advanced Topics**:  
   - Multithreading  
   - JDBC (Database)  
   - JavaFX (GUI)  

---

### **📌 Recommended Resources**
- **Books**:  
  - *Head First Java* (Beginner-friendly)  
  - *Java: A Beginner’s Guide* by Herbert Schildt  
- **Online Courses**:  
  - [Java for Beginners (Udemy)](https://www.udemy.com/topic/java/)  
  - [Java Programming (MOOC)](https://java-programming.mooc.fi/)  

---

### **❓ Need Help?**
- Ask me for **code examples**, **debugging help**, or **project ideas**!  
- Want a **deeper dive** into any topic? Let me know! 🚀  

Happy coding! 😊

Java Learn Beginner

Learning Java as a beginner is an exciting journey! Below is a **step-by-step beginner-friendly guide** to mastering Java fundamentals with clear explanations and practical examples.  

---

## **📌 1. Introduction to Java**
- **What is Java?**  
  - A **high-level**, **object-oriented** programming language.  
  - Runs on the **JVM (Java Virtual Machine)**, making it **platform-independent**.  
  - Used in Android apps, web backends, desktop apps, and more.  

- **Key Features**:  
  - Simple, secure, portable, multithreaded, and robust.  

---

## **🛠 2. Setting Up Java**
1. **Install JDK (Java Development Kit)**  
   - Download from [Oracle JDK](https://www.oracle.com/java/technologies/javase-downloads.html) or [OpenJDK](https://openjdk.org/).  
   - Set `JAVA_HOME` environment variable.  

2. **Verify Installation**  
   ```bash
   java -version   # Check Java version
   javac -version  # Check compiler version
   ```

3. **Write Your First Program**  
   ```java
   public class HelloWorld {
       public static void main(String[] args) {
           System.out.println("Hello, World!");
       }
   }
   ```
   - Save as `HelloWorld.java`.  
   - Compile: `javac HelloWorld.java`  
   - Run: `java HelloWorld`  

---

## **📝 3. Basic Syntax & Structure**
- **Case-Sensitive**: `Hello` ≠ `hello`.  
- **Class Name** must match the filename (`HelloWorld.java` → `public class HelloWorld`).  
- **`main` method** is the program’s entry point.  

---

## **🔢 4. Variables & Data Types**
### **Primitive Data Types**
| Type      | Example           | Size    |
|-----------|-------------------|---------|
| `int`     | `int age = 25;`   | 4 bytes |
| `double`  | `double pi = 3.14;`| 8 bytes |
| `char`    | `char grade = 'A';`| 2 bytes |
| `boolean` | `boolean isJavaFun = true;` | 1 bit |

### **Non-Primitive Types**
- `String` (text)  
  ```java
  String name = "Alice";
  ```
- **Arrays** (fixed-size collection)  
  ```java
  int[] numbers = {1, 2, 3};
  String[] fruits = {"Apple", "Banana"};
  ```

---

## **🔧 5. Operators**
| Type        | Operators                     | Example                     |
|-------------|-------------------------------|-----------------------------|
| Arithmetic  | `+`, `-`, `*`, `/`, `%`       | `int sum = 5 + 3;` → `8`    |
| Comparison  | `==`, `!=`, `>`, `<`, `>=`, `<=` | `if (age >= 18) { ... }`    |
| Logical     | `&&` (AND), `||` (OR), `!` (NOT) | `if (isStudent && hasID) { ... }` |
| Assignment  | `=`, `+=`, `-=`, `*=`         | `x += 5;` → `x = x + 5;`    |

---

## **🔄 6. Control Flow (Conditionals & Loops)**
### **If-Else**
```java
int age = 20;
if (age >= 18) {
    System.out.println("Adult");
} else {
    System.out.println("Minor");
}
```

### **Switch-Case**
```java
int day = 3;
switch (day) {
    case 1: System.out.println("Monday"); break;
    case 2: System.out.println("Tuesday"); break;
    default: System.out.println("Invalid day");
}
```

### **Loops**
#### **For Loop**
```java
for (int i = 0; i < 5; i++) {
    System.out.println(i); // Prints 0 to 4
}
```

#### **While Loop**
```java
int i = 0;
while (i < 5) {
    System.out.println(i);
    i++;
}
```

#### **Do-While Loop**
```java
int i = 0;
do {
    System.out.println(i);
    i++;
} while (i < 5);
```

---

## **📦 7. Methods (Functions)**
```java
public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }

    public static void main(String[] args) {
        int result = add(5, 3);
        System.out.println("Sum: " + result); // Output: 8
    }
}
```
- **`void`** → Method doesn’t return anything.  
- **`static`** → Can be called without creating an object.  

---

## **🧩 8. Object-Oriented Programming (OOP)**
### **Class & Object**
```java
class Dog {
    String name;  // Field (attribute)

    void bark() {  // Method
        System.out.println(name + " says Woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog();  // Create object
        myDog.name = "Buddy";
        myDog.bark();  // Output: Buddy says Woof!
    }
}
```

### **4 OOP Concepts**
1. **Encapsulation** → Hide data (`private` fields + `getter/setter`).  
2. **Inheritance** → Reuse code (`extends` keyword).  
3. **Polymorphism** → Same method, different forms (overriding/overloading).  
4. **Abstraction** → Hide complexity (`abstract` classes/interfaces).  

---

## **🚨 9. Exception Handling**
```java
try {
    int result = 10 / 0;  // Throws ArithmeticException
} catch (ArithmeticException e) {
    System.out.println("Error: " + e.getMessage());
} finally {
    System.out.println("This always runs.");
}
```

---

## **📚 10. Collections Framework**
| Type      | Example                          | Description                  |
|-----------|----------------------------------|------------------------------|
| `ArrayList` | `List<String> names = new ArrayList<>();` | Dynamic-size list |
| `HashMap`  | `Map<String, Integer> ages = new HashMap<>();` | Key-value pairs |

```java
List<String> fruits = new ArrayList<>();
fruits.add("Apple");
fruits.add("Banana");
System.out.println(fruits.get(0)); // Output: Apple
```

---

## **📂 11. File Handling**
```java
import java.io.File;
import java.io.FileWriter;

public class FileExample {
    public static void main(String[] args) {
        try {
            File file = new File("test.txt");
            FileWriter writer = new FileWriter(file);
            writer.write("Hello, Java!");
            writer.close();
        } catch (Exception e) {
            System.out.println("Error: " + e);
        }
    }
}
```

---

## **🚀 Next Steps**
1. **Practice** on [HackerRank](https://www.hackerrank.com/domains/tutorials/10-days-of-java) or [LeetCode](https://leetcode.com/).  
2. **Build Projects**:  
   - Calculator  
   - To-Do List App  
   - Simple Game (e.g., Tic-Tac-Toe)  
3. **Learn Advanced Topics**:  
   - Multithreading  
   - JDBC (Database)  
   - JavaFX (GUI)  

---

### **📌 Recommended Resources**
- **Books**:  
  - *Head First Java* (Beginner-friendly)  
  - *Java: A Beginner’s Guide* by Herbert Schildt  
- **Online Courses**:  
  - [Java for Beginners (Udemy)](https://www.udemy.com/topic/java/)  
  - [Java Programming (MOOC)](https://java-programming.mooc.fi/)  

---

### **❓ Need Help?**
- Ask me for **code examples**, **debugging help**, or **project ideas**!  
- Want a **deeper dive** into any topic? Let me know! 🚀  

Happy coding! 😊

Java Learn Basic

Learning Java from the basics is a great choice! Java is a versatile, object-oriented programming language widely used for Android development, web applications, enterprise systems, and more. Below is a structured roadmap to learn Java fundamentals:

---

### **1. Introduction to Java**
- **What is Java?**  
  - Platform-independent (Write Once, Run Anywhere - WORA)
  - Object-oriented, robust, secure, and multithreaded
- **Java Editions**: SE (Standard Edition), EE (Enterprise Edition), ME (Micro Edition)
- **JDK vs. JRE vs. JVM**  
  - **JDK (Java Development Kit)**: Tools to develop Java programs (compiler, debugger, etc.).  
  - **JRE (Java Runtime Environment)**: Runs compiled Java programs.  
  - **JVM (Java Virtual Machine)**: Executes bytecode.

---

### **2. Setting Up the Environment**
1. **Install JDK** (from [Oracle](https://www.oracle.com/java/technologies/javase-downloads.html) or OpenJDK).
2. **Set `JAVA_HOME`** environment variable.
3. **Verify Installation**:  
   ```bash
   java -version
   javac -version
   ```
4. **Use an IDE** (e.g., IntelliJ IDEA, Eclipse, or VS Code) or a simple text editor.

---

### **3. Basic Syntax & Structure**
```java
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}
```
- **Class**: `HelloWorld` is a class (file name must match the class name).
- **`main` method**: Entry point of the program.
- **`System.out.println()`**: Prints output to the console.

---

### **4. Data Types & Variables**
- **Primitive Types**:  
  ```java
  int num = 10;          // Integer
  double pi = 3.14;      // Floating-point
  char letter = 'A';     // Character
  boolean flag = true;   // Boolean
  ```
- **Non-Primitive Types**: `String`, arrays, classes.
- **Variable Naming Rules**:  
  - Start with a letter, `_`, or `$`.
  - Case-sensitive (`age` ≠ `Age`).

---

### **5. Operators**
- **Arithmetic**: `+`, `-`, `*`, `/`, `%` (modulus).
- **Comparison**: `==`, `!=`, `>`, `<`, `>=`, `<=`.
- **Logical**: `&&` (AND), `||` (OR), `!` (NOT).
- **Assignment**: `=`, `+=`, `-=`.

---

### **6. Control Flow**
#### **Conditionals**
```java
if (age >= 18) {
    System.out.println("Adult");
} else {
    System.out.println("Minor");
}
```
- **`switch` Statement**:
  ```java
  switch (day) {
      case 1: System.out.println("Monday"); break;
      default: System.out.println("Invalid day");
  }
  ```

#### **Loops**
- **`for` Loop**:
  ```java
  for (int i = 0; i < 5; i++) {
      System.out.println(i);
  }
  ```
- **`while` Loop**:
  ```java
  while (i < 5) {
      System.out.println(i);
      i++;
  }
  ```
- **`do-while` Loop**:
  ```java
  do {
      System.out.println(i);
      i++;
  } while (i < 5);
  ```

---

### **7. Arrays**
```java
int[] numbers = {1, 2, 3};
String[] names = new String[3]; // Fixed size
```
- **Access Elements**: `numbers[0]` → `1`.
- **Loop Through Array**:
  ```java
  for (int num : numbers) {
      System.out.println(num);
  }
  ```

---

### **8. Methods (Functions)**
```java
public static int add(int a, int b) {
    return a + b;
}
```
- **Calling a Method**:  
  ```java
  int sum = add(5, 3); // Returns 8
  ```
- **Method Overloading**: Same name, different parameters.

---

### **9. Object-Oriented Programming (OOP)**
#### **Classes & Objects**
```java
class Dog {
    String name;  // Field

    void bark() {  // Method
        System.out.println(name + " says Woof!");
    }
}

// Create an object
Dog myDog = new Dog();
myDog.name = "Buddy";
myDog.bark();
```

#### **4 OOP Pillars**:
1. **Encapsulation**: Hide data (use `private` fields + `getter/setter` methods).
2. **Inheritance**:  
   ```java
   class Animal { void eat() { ... } }
   class Dog extends Animal { ... }
   ```
3. **Polymorphism**:  
   - Method overriding (same method, different implementation in child class).  
   - Method overloading (same name, different parameters).
4. **Abstraction**:  
   - Abstract classes (`abstract class Animal { ... }`).  
   - Interfaces (`interface Drawable { void draw(); }`).

---

### **10. Exception Handling**
```java
try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero!");
} finally {
    System.out.println("Cleanup code here.");
}
```

---

### **11. Collections Framework**
- **Lists**: Ordered, allows duplicates (`ArrayList`, `LinkedList`).
  ```java
  List<String> fruits = new ArrayList<>();
  fruits.add("Apple");
  ```
- **Sets**: No duplicates (`HashSet`, `TreeSet`).
- **Maps**: Key-value pairs (`HashMap`, `TreeMap`).
  ```java
  Map<String, Integer> ages = new HashMap<>();
  ages.put("Alice", 25);
  ```

---

### **12. File I/O**
```java
import java.io.File;
import java.io.FileWriter;

File file = new File("test.txt");
try (FileWriter writer = new FileWriter(file)) {
    writer.write("Hello, File!");
}
```

---

### **13. Multithreading**
```java
class MyThread extends Thread {
    public void run() {
        System.out.println("Thread is running.");
    }
}

MyThread t1 = new MyThread();
t1.start();
```

---

### **Next Steps**
1. **Practice**: Solve problems on platforms like LeetCode, HackerRank.
2. **Build Projects**: Calculator, To-Do List, Simple Game.
3. **Explore Advanced Topics**:  
   - JavaFX (GUI).  
   - JDBC (Database connectivity).  
   - Spring Framework (Enterprise Java).

---

### **Recommended Resources**
- **Books**:  
  - *Head First Java* (Beginner-friendly).  
  - *Effective Java* by Joshua Bloch (Best practices).  
- **Online Courses**:  
  - MOOC by University of Helsinki ([Java Programming](https://java-programming.mooc.fi/)).  
  - Coursera/Udemy courses.  
- **Documentation**: [Oracle Java Docs](https://docs.oracle.com/en/java/).

---

Would you like a deeper dive into any specific topic or hands-on examples? Let me know how I can assist further!

Java Inheritance

# Understanding Java Keywords: `public`, `void`, `class`, `super`, and `final`

These are all fundamental Java keywords that serve different purposes in the language. Let me explain each one clearly with examples:

## 1. `public` - Access Modifier
Controls the visibility/accessibility of classes, methods, and variables.

```java
public class MyClass {       // Class accessible from anywhere
    public int myVariable;   // Variable accessible from anywhere
    
    public void myMethod() { // Method accessible from anywhere
        System.out.println("Public method");
    }
}
```

## 2. `void` - Return Type
Indicates a method doesn't return any value.

```java
public class Calculator {
    // This method performs an action but returns nothing
    public void printSum(int a, int b) {
        System.out.println("Sum: " + (a + b));
    }
    
    // Contrast with a method that returns a value
    public int calculateSum(int a, int b) {
        return a + b;
    }
}
```

## 3. `class` - Class Declaration
Used to define a new class (blueprint for objects).

```java
class Animal {          // Class declaration
    String name;        // Field
    
    void makeSound() {  // Method
        System.out.println("Some sound");
    }
}
```

## 4. `super` - Parent Class Reference
Used to access parent class members (fields, methods, constructors).

```java
class Vehicle {
    int maxSpeed = 120;
    
    void display() {
        System.out.println("Vehicle display");
    }
}

class Car extends Vehicle {
    int maxSpeed = 180;
    
    void display() {
        super.display(); // Calls parent's display()
        System.out.println("Car max speed: " + maxSpeed);
        System.out.println("Vehicle max speed: " + super.maxSpeed);
    }
    
    Car() {
        super(); // Calls parent's constructor (implicit if not written)
    }
}
```

## 5. `final` - Non-modifiable Declaration
Makes variables constant, methods non-overridable, or classes non-inheritable.

```java
final class FinalClass {    // Cannot be extended
    final int MAX_VALUE = 100; // Constant variable
    
    final void display() {  // Cannot be overridden
        System.out.println("This is final");
    }
}

// This would cause a compile error:
// class ChildClass extends FinalClass {}
```

## Combined Usage Example

Here's an example showing all these keywords working together:

```java
public class Parent {          // public class
    final String FAMILY_NAME = "Smith"; // final variable
    
    public void display() {    // public void method
        System.out.println("Family: " + FAMILY_NAME);
    }
}

public class Child extends Parent {
    private String firstName;
    
    public Child(String name) { // public constructor
        this.firstName = name;
    }
    
    @Override
    public void display() {    // overriding parent's method
        super.display();       // using super to call parent's method
        System.out.println("First name: " + firstName);
    }
    
    // This would cause error because display() is final in Parent
    // public final void display() {}
}

public class Main {
    public static void main(String[] args) {
        Child child = new Child("John");
        child.display();
    }
}
```

## Key Differences Summary

| Keyword | Purpose | Example Use |
|---------|---------|-------------|
| `public` | Makes class/member accessible from anywhere | `public class MyClass` |
| `void`   | Indicates no return value | `public void doSomething()` |
| `class`  | Declares a new class | `class MyClass` |
| `super`  | Refers to parent class | `super.methodCall()` |
| `final`  | Makes something unchangeable | `final int MAX = 100` |

These keywords are fundamental to Java programming and understanding them is crucial for writing proper object-oriented code.

Java Inheritance

# Java Inheritance: Complete Guide with Examples

Inheritance is one of the fundamental concepts of object-oriented programming (OOP) in Java. It allows a class to inherit properties and behaviors (fields and methods) from another class.

## Basic Inheritance Syntax

```java
class ParentClass {
    // fields and methods
}

class ChildClass extends ParentClass {
    // additional fields and methods
}
```

## Key Concepts of Inheritance

### 1. Single Inheritance
Java supports single inheritance (a class can extend only one parent class).

```java
class Animal {
    void eat() {
        System.out.println("Eating...");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Barking...");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();
        d.eat();  // Inherited from Animal
        d.bark(); // Defined in Dog
    }
}
```

### 2. Multilevel Inheritance
A class can inherit from another class which itself inherits from another class.

```java
class Animal {
    void eat() {
        System.out.println("Eating...");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Barking...");
    }
}

class Puppy extends Dog {
    void weep() {
        System.out.println("Weeping...");
    }
}

public class Main {
    public static void main(String[] args) {
        Puppy p = new Puppy();
        p.eat();  // From Animal
        p.bark(); // From Dog
        p.weep(); // From Puppy
    }
}
```

### 3. Hierarchical Inheritance
Multiple classes inherit from a single parent class.

```java
class Animal {
    void eat() {
        System.out.println("Eating...");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Barking...");
    }
}

class Cat extends Animal {
    void meow() {
        System.out.println("Meowing...");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();
        d.eat();  // From Animal
        d.bark(); // From Dog
        
        Cat c = new Cat();
        c.eat();  // From Animal
        c.meow(); // From Cat
    }
}
```

### 4. Method Overriding
Child class can provide its own implementation of a method that is already defined in its parent class.

```java
class Animal {
    void makeSound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Dog barks");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal a = new Animal();
        a.makeSound(); // Output: Animal makes a sound
        
        Dog d = new Dog();
        d.makeSound(); // Output: Dog barks
    }
}
```

### 5. The `super` Keyword
Used to refer to immediate parent class instance variable, method, or constructor.

```java
class Vehicle {
    int maxSpeed = 120;
}

class Car extends Vehicle {
    int maxSpeed = 180;
    
    void display() {
        System.out.println("Maximum Speed: " + super.maxSpeed); // Parent class
        System.out.println("Maximum Speed: " + maxSpeed);       // Current class
    }
}

public class Main {
    public static void main(String[] args) {
        Car c = new Car();
        c.display();
    }
}
```

### 6. Inheritance with Constructors
Parent class constructor is called before child class constructor.

```java
class Parent {
    Parent() {
        System.out.println("Parent constructor");
    }
}

class Child extends Parent {
    Child() {
        super(); // Implicitly called if not written
        System.out.println("Child constructor");
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
    }
}
```

### 7. `final` Keyword and Inheritance
- `final` class cannot be inherited
- `final` method cannot be overridden

```java
final class FinalClass {
    // Cannot be inherited
}

class Parent {
    final void display() {
        System.out.println("This cannot be overridden");
    }
}

class Child extends Parent {
    // This would cause a compile error:
    // void display() { System.out.println("Trying to override"); }
}
```

## When to Use Inheritance

1. **IS-A relationship**: When a class "is a" specialized version of another class
   - Dog IS-A Animal
   - Car IS-A Vehicle

2. **Code reusability**: When you want to reuse existing code with additional features

3. **Polymorphism**: When you need to implement runtime polymorphism through method overriding

## Important Points

1. Java doesn't support multiple inheritance with classes (but supports with interfaces)
2. Private members are not inherited
3. Constructors are not inherited
4. All classes in Java implicitly inherit from `Object` class
5. Use `@Override` annotation to explicitly indicate method overriding

## Practical Example: Employee Management System

```java
class Employee {
    private String name;
    private double salary;
    
    public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }
    
    public void displayDetails() {
        System.out.println("Name: " + name);
        System.out.println("Salary: $" + salary);
    }
    
    public double calculateBonus() {
        return salary * 0.05; // 5% bonus
    }
}

class Manager extends Employee {
    private String department;
    
    public Manager(String name, double salary, String department) {
        super(name, salary);
        this.department = department;
    }
    
    @Override
    public void displayDetails() {
        super.displayDetails();
        System.out.println("Department: " + department);
    }
    
    @Override
    public double calculateBonus() {
        return super.calculateBonus() + 1000; // Extra $1000 for managers
    }
}

public class Main {
    public static void main(String[] args) {
        Employee emp = new Employee("John Doe", 50000);
        Manager mgr = new Manager("Jane Smith", 80000, "IT");
        
        emp.displayDetails();
        System.out.println("Bonus: $" + emp.calculateBonus());
        
        System.out.println();
        
        mgr.displayDetails();
        System.out.println("Bonus: $" + mgr.calculateBonus());
    }
}
```

This example demonstrates how inheritance allows us to extend the basic `Employee` class to create a specialized `Manager` class with additional properties and behaviors while reusing existing code.

Java Server LBJLI

# Complete Java File Editor with Network Integration

Here's a comprehensive solution that:
1. Connects to a network server
2. Uses JFileChooser to load/edit local text files
3. Downloads files to the connected server

Java Download

# Using JFileChooser to Load, Edit, and Download Text Files in Java

Here's a complete example of how to use JFileChooser to load a text file from the local system, edit it, and then save/download it (either locally or to a network location):

```java
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;

public class FileEditor extends JFrame {
    private JTextArea textArea;
    private JFileChooser fileChooser;
    private File currentFile;

    public FileEditor() {
        setTitle("Text File Editor");
        setSize(600, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        
        // Create components
        textArea = new JTextArea();
        JScrollPane scrollPane = new JScrollPane(textArea);
        JButton openButton = new JButton("Open");
        JButton saveButton = new JButton("Save");
        JButton saveAsButton = new JButton("Save As");
        JButton downloadButton = new JButton("Download to Server");
        
        // Create panel for buttons
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(openButton);
        buttonPanel.add(saveButton);
        buttonPanel.add(saveAsButton);
        buttonPanel.add(downloadButton);
        
        // Add components to frame
        add(scrollPane, BorderLayout.CENTER);
        add(buttonPanel, BorderLayout.SOUTH);
        
        // Initialize file chooser
        fileChooser = new JFileChooser();
        fileChooser.setFileFilter(new javax.swing.filechooser.FileNameExtensionFilter("Text Files", "txt"));
        
        // Add action listeners
        openButton.addActionListener(e -> openFile());
        saveButton.addActionListener(e -> saveFile());
        saveAsButton.addActionListener(e -> saveFileAs());
        downloadButton.addActionListener(e -> downloadToServer());
    }
    
    private void openFile() {
        int returnVal = fileChooser.showOpenDialog(this);
        if (returnVal == JFileChooser.APPROVE_OPTION) {
            currentFile = fileChooser.getSelectedFile();
            try (BufferedReader reader = new BufferedReader(new FileReader(currentFile))) {
                StringBuilder content = new StringBuilder();
                String line;
                while ((line = reader.readLine()) != null) {
                    content.append(line).append("\n");
                }
                textArea.setText(content.toString());
            } catch (IOException e) {
                JOptionPane.showMessageDialog(this, "Error reading file: " + e.getMessage(), 
                    "Error", JOptionPane.ERROR_MESSAGE);
            }
        }
    }
    
    private void saveFile() {
        if (currentFile == null) {
            saveFileAs();
            return;
        }
        
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(currentFile))) {
            writer.write(textArea.getText());
            JOptionPane.showMessageDialog(this, "File saved successfully!");
        } catch (IOException e) {
            JOptionPane.showMessageDialog(this, "Error saving file: " + e.getMessage(), 
                "Error", JOptionPane.ERROR_MESSAGE);
        }
    }
    
    private void saveFileAs() {
        int returnVal = fileChooser.showSaveDialog(this);
        if (returnVal == JFileChooser.APPROVE_OPTION) {
            currentFile = fileChooser.getSelectedFile();
            // Ensure the file has .txt extension
            if (!currentFile.getName().toLowerCase().endsWith(".txt")) {
                currentFile = new File(currentFile.getAbsolutePath() + ".txt");
            }
            saveFile();
        }
    }
    
    private void downloadToServer() {
        if (textArea.getText().isEmpty()) {
            JOptionPane.showMessageDialog(this, "No content to download!", 
                "Warning", JOptionPane.WARNING_MESSAGE);
            return;
        }
        
        // Example server URL - replace with your actual server endpoint
        String serverUrl = "http://yourserver.com/upload.php";
        
        try {
            // Create connection
            URL url = new URL(serverUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("POST");
            connection.setDoOutput(true);
            
            // Write content to output stream
            try (OutputStream os = connection.getOutputStream();
                 OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8")) {
                osw.write(textArea.getText());
                osw.flush();
            }
            
            // Check response
            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                JOptionPane.showMessageDialog(this, "File successfully downloaded to server!");
            } else {
                JOptionPane.showMessageDialog(this, "Server returned error: " + responseCode, 
                    "Error", JOptionPane.ERROR_MESSAGE);
            }
        } catch (Exception e) {
            JOptionPane.showMessageDialog(this, "Error downloading to server: " + e.getMessage(), 
                "Error", JOptionPane.ERROR_MESSAGE);
        }
    }
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            FileEditor editor = new FileEditor();
            editor.setVisible(true);
        });
    }
}
```

## Key Features Explained:

1. **JFileChooser**:
   - Used for both opening and saving files
   - Configured to only show .txt files with `setFileFilter()`

2. **File Operations**:
   - `openFile()`: Reads the selected file and displays content in the text area
   - `saveFile()`: Saves content to the current file
   - `saveFileAs()`: Allows saving to a new file location

3. **Network Download**:
   - `downloadToServer()`: Demonstrates how to send the text content to a server via HTTP POST
   - You'll need to replace the example URL with your actual server endpoint

4. **Error Handling**:
   - All operations include try-catch blocks to handle potential IO errors
   - User is notified of errors via `JOptionPane`

## To Use This Code:

1. For local file operations, just run the program - it will work with any text files on your system.

2. For the network download functionality:
   - You'll need a server endpoint that can receive the file
   - The example shows a simple HTTP POST request
   - You may need to modify the request format based on your server requirements

3. Make sure your Android Java compiler has network permissions if you're using the download feature.

Would you like me to explain any specific part in more detail or modify any aspect of this implementation?