# 📚 Java Programming Language – Part 3/10: Methods & Functions
#Java #Programming #Methods #Functions #OOP

Welcome to Part 3 of our Java series! Today we'll dive into methods - the building blocks of Java programs.

---

## 🔹 What are Methods in Java?
Methods are blocks of code that:
✔️ Perform specific tasks
✔️ Can be reused multiple times
✔️ Help organize code logically
✔️ Can return a value or perform actions without returning

// Method structure
[access-modifier] [static] return-type methodName(parameters) {
    // method body
    return value; // if not void
}

---

## 🔹 Method Components
### 1. Simple Method Example

public class Calculator {
    
    // Method without return (void)
    public static void greet() {
        System.out.println("Welcome to Calculator!");
    }
    
    // Method with return
    public static int add(int a, int b) {
        return a + b;
    }
    
    public static void main(String[] args) {
        greet();  // Calling void method
        int sum = add(5, 3);  // Calling return method
        System.out.println("Sum: " + sum);
    }
}

### 2. Method Parameters

public static void printUserInfo(String name, int age) {
    System.out.println("Name: " + name);
    System.out.println("Age: " + age);
}

### 3. Return Values

public static boolean isAdult(int age) {
    return age >= 18;
}

---

## 🔹 Method Overloading
Multiple methods with same name but different parameters.

public class MathOperations {
    
    // Version 1: Add two integers
    public static int add(int a, int b) {
        return a + b;
    }
    
    // Version 2: Add three integers
    public static int add(int a, int b, int c) {
        return a + b + c;
    }
    
    // Version 3: Add two doubles
    public static double add(double a, double b) {
        return a + b;
    }
    
    public static void main(String[] args) {
        System.out.println(add(2, 3));       // 5
        System.out.println(add(2, 3, 4));    // 9
        System.out.println(add(2.5, 3.7));  // 6.2
    }
}

---

## 🔹 Recursion
A method that calls itself.

### 1. Factorial Example

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

### 2. Fibonacci Sequence

public static int fibonacci(int n) {
    if (n <= 1) {
        return n;
    }
    return fibonacci(n-1) + fibonacci(n-2);
}

---

## 🔹 Variable Scope
Variables have different scope depending on where they're declared.

public class ScopeExample {
    static int classVar = 10;  // Class-level variable
    
    public static void methodExample() {
        int methodVar = 20;  // Method-level variable
        System.out.println(classVar);  // Accessible
        System.out.println(methodVar); // Accessible
    }
    
    public static void main(String[] args) {
        int mainVar = 30;  // Block-level variable
        System.out.println(classVar);  // Accessible
        // System.out.println(methodVar); // ERROR - not accessible
        System.out.println(mainVar);   // Accessible
    }
}

---

## 🔹 Practical Example: Temperature Converter

public class TemperatureConverter {
    
    public static double celsiusToFahrenheit(double celsius) {
        return (celsius * 9/5) + 32;
    }
    
    public static double fahrenheitToCelsius(double fahrenheit) {
        return (fahrenheit - 32) * 5/9;
    }
    
    public static void main(String[] args) {
        System.out.println("20°C to Fahrenheit: " + celsiusToFahrenheit(20));
        System.out.println("68°F to Celsius: " + fahrenheitToCelsius(68));
    }
}

---

## 🔹 Best Practices for Methods
1. Single Responsibility Principle - Each method should do one thing
2. Descriptive Names - Use verbs (calculateTotal, validateInput)
3. Limit Parameters - Ideally 3-4 parameters max
4. Proper Indentation - Keep code readable
5. Documentation - Use JavaDoc comments

# 📚 Java Programming Language – Part 4/10: Object-Oriented Programming (OOP) Basics
#Java #OOP #Programming #Classes #Objects

Welcome to Part 4 of our Java series! Today we'll explore the fundamentals of Object-Oriented Programming in Java.

---

## 🔹 What is OOP?
Object-Oriented Programming is a paradigm based on:
- Objects (instances of classes)
- Classes (blueprints for objects)
- 4 Main Principles:
- Encapsulation
- Inheritance
- Polymorphism
- Abstraction

---

## 🔹 Classes and Objects

### 1. Class Definition

public class Car {
    // Fields (attributes)
    String brand;
    String model;
    int year;
    
    // Method
    public void startEngine() {
        System.out.println("Engine started!");
    }
}

### 2. Creating Objects

public class Main {
    public static void main(String[] args) {
        // Creating an object
        Car myCar = new Car();
        
        // Accessing fields
        myCar.brand = "Toyota";
        myCar.model = "Corolla";
        myCar.year = 2022;
        
        // Calling method
        myCar.startEngine();
    }
}

---

## 🔹 Constructors
Special methods called when an object is instantiated.

### 1. Default Constructor

public class Car {
    // Default constructor (created automatically if none exists)
    public Car() {
    }
}

### 2. Parameterized Constructor

public class Car {
    String brand;
    String model;
    int year;
    
    public Car(String brand, String model, int year) {
        this.brand = brand;
        this.model = model;
        this.year = year;
    }
}

// Usage:
Car myCar = new Car("Toyota", "Corolla", 2022);

### 3. Constructor Overloading

public class Car {
    // Constructor 1
    public Car() {
        this.brand = "Unknown";
    }
    
    // Constructor 2
    public Car(String brand) {
        this.brand = brand;
    }
}

---

## 🔹 Encapsulation
Protecting data by making fields private and providing public getters/setters.

public class BankAccount {
    private double balance;  // Private field
    
    // Public getter
    public double getBalance() {
        return balance;
    }
    
    // Public setter with validation
    public void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
        }
    }
}

---

## 🔹 'this' Keyword
Refers to the current object instance.

public class Person {
    private String name;
    
    public Person(String name) {
        this.name = name;  // 'this' distinguishes field from parameter
    }
}

---

## 🔹 Practical Example: Student Management System

public class Student {
    private String id;
    private String name;
    private double gpa;
    
    public Student(String id, String name) {
        this.id = id;
        this.name = name;
    }
    
    // Getters and setters
    public String getId() { return id; }
    public String getName() { return name; }
    public double getGpa() { return gpa; }
    
    public void updateGpa(double newGpa) {
        if (newGpa >= 0 && newGpa <= 4.0) {
            this.gpa = newGpa;
        }
    }
    
    public void printInfo() {
        System.out.printf("ID: %s, Name: %s, GPA: %.2f\n", 
                         id, name, gpa);
    }
}

// Usage:
Student student1 = new Student("S1001", "Ahmed");
student1.updateGpa(3.75);
student1.printInfo();

---

## 🔹 Static vs Instance Members

| Feature | Static | Instance |
|---------------|---------------------------|---------------------------|
| Belongs to | Class | Object |
| Memory | Once per class | Each object has its own |
| Access | ClassName.member | object.iss.onember |
| Example | Math.PI | student.getName() |

public class Counter {
    static int count = 0;  // Shared across all instances
    int instanceCount = 0; // Unique to each object
    
    public Counter() {
        count++;
        instanceCount++;
    }
    
    public static void printCount() {
        System.out.println("Total count: " + count);
    }
}

---

### 📌 What's Next?
In Part 5, we'll cover:
➡️ Inheritance
➡️ Method Overriding
➡️ super Keyword
➡️ Abstract Classes

#JavaOOP #ObjectOriented #ProgrammingBasics 🚀

# 📚 Java Programming Language – Part 5/10: Inheritance & Polymorphism
#Java #OOP #Inheritance #Polymorphism #Programming

Welcome to Part 5 of our Java series! Today we'll explore two fundamental OOP concepts: Inheritance and Polymorphism.

---

## 🔹 Inheritance in Java
Inheritance allows a class to acquire properties and methods of another class.

### 1. Basic Inheritance Syntax

// Parent class (Superclass)
class Vehicle {
    String brand;
    
    public void start() {
        System.out.println("Vehicle starting...");
    }
}

// Child class (Subclass)
class Car extends Vehicle {  // 'extends' keyword
    int numberOfDoors;
    
    public void honk() {
        System.out.println("Beep beep!");
    }
}

// Usage:
Car myCar = new Car();
myCar.brand = "Toyota";  // Inherited from Vehicle
myCar.start();          // Inherited method
myCar.honk();           // Child's own method

### 2. Inheritance Types
Java supports:
- Single Inheritance (One parent → one child)
- Multilevel Inheritance (Grandparent → parent → child)
- Hierarchical Inheritance (One parent → multiple children)

*Note: Java doesn't support multiple inheritance with classes*

---

## 🔹 Method Overriding
Subclass can provide its own implementation of an inherited method.

class Vehicle {
    public void start() {
        System.out.println("Vehicle starting...");
    }
}

class ElectricCar extends Vehicle {
    @Override  // Annotation (optional but recommended)
    public void start() {
        System.out.println("Electric car starting silently...");
    }
}

---

## 🔹 super Keyword
Used to access superclass members from subclass.

### 1. Accessing Superclass Methods

class ElectricCar extends Vehicle {
    @Override
    public void start() {
        super.start();  // Calls Vehicle's start()
        System.out.println("Battery check complete");
    }
}

### 2. Superclass Constructor

class Vehicle {
    String brand;
    
    public Vehicle(String brand) {
        this.brand = brand;
    }
}

class Car extends Vehicle {
    int doors;
    
    public Car(String brand, int doors) {
        super(brand);  // Must be first statement
        this.doors = doors;
    }
}

---

## 🔹 Polymorphism
"Many forms" - ability of an object to take many forms.

### 1. Compile-time Polymorphism (Method Overloading)

class Calculator {
    // Same method name, different parameters
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }
}

### 2. Runtime Polymorphism (Method Overriding)

Vehicle v1 = new Vehicle();  // Parent reference, parent object
Vehicle v2 = new Car();      // Parent reference, child object

v1.start();  // Calls Vehicle's start()
v2.start();  // Calls Car's start() if overridden

---

## 🔹 final Keyword
Restricts inheritance and overriding.

final class CannotBeExtended { }  // Cannot be inherited

class Parent {
    final void cannotOverride() { }  // Cannot be overridden
}

---

## 🔹 Object Class
All classes implicitly extend Java's Object class.

Important methods:
- toString() - String representation
- equals() - Compare objects
- hashCode() - Hash code value

class MyClass { }  // Automatically extends Object

MyClass obj = new MyClass();
System.out.println(obj.toString());  // Outputs something like MyClass@1dbd16a6

---

# 📚 Java Programming Language – Part 6/10: Interfaces & Abstract Classes
#Java #OOP #Interfaces #AbstractClasses #Programming

Welcome to Part 6 of our Java series! Today we'll explore two crucial concepts for achieving abstraction in Java: Interfaces and Abstract Classes.

---

## 🔹 Interfaces in Java
Interfaces define contracts that classes must implement (100% abstraction).

### 1. Interface Declaration (Pre-Java 8)

interface Drawable {
    // Constant fields (implicitly public static final)
    String COLOR = "Black";
    
    // Abstract methods (implicitly public abstract)
    void draw();
    double calculateArea();
}

### 2. Implementing Interfaces

class Circle implements Drawable {
    private double radius;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    @Override
    public void draw() {
        System.out.println("Drawing a circle");
    }
    
    @Override
    public double calculateArea() {
        return Math.PI * radius * radius;
    }
}

### 3. Modern Interfaces (Java 8+) Features

interface Vehicle {
    // Traditional abstract method
    void start();
    
    // Default method (with implementation)
    default void honk() {
        System.out.println("Beep beep!");
    }
    
    // Static method
    static void printType() {
        System.out.println("I'm a vehicle");
    }
}

---

## 🔹 Abstract Classes
Classes that can't be instantiated and may contain abstract methods.

### 1. Abstract Class Example

abstract class Animal {
    // Concrete method
    public void breathe() {
        System.out.println("Breathing...");
    }
    
    // Abstract method (no implementation)
    public abstract void makeSound();
}

### 2. Extending Abstract Classes

class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Woof woof!");
    }
}

// Usage:
Animal myPet = new Dog();
myPet.breathe();    // Inherited concrete method
myPet.makeSound();  // Implemented abstract method

---

## 🔹 Key Differences

| Feature | Interface | Abstract Class |
|------------------------|-----------------------------------|------------------------------------|
| Instantiation | Cannot be instantiated | Cannot be instantiated |
| Methods | All abstract (pre-Java 8) | Can have both abstract & concrete |
| Variables | Only constants | Any variables |
| Multiple Inheritance | Class can implement many interfaces | Class extends only one abstract class |
| Default Methods | Supported (Java 8+) | Not applicable |
| Constructor | No constructors | Can have constructors |
| When to Use | Define contracts/APIs | Share code among related classes |

---

## 🔹 Practical Example: Payment System

interface PaymentMethod {
    void processPayment(double amount);
    boolean validate();
}

abstract class OnlinePayment implements PaymentMethod {
    protected String cardNumber;
    
    public OnlinePayment(String cardNumber) {
        this.cardNumber = cardNumber;
    }
    
    @Override
    public boolean validate() {
        return cardNumber != null && cardNumber.length() == 16;
    }
}

class CreditCardPayment extends OnlinePayment {
    public CreditCardPayment(String cardNumber) {
        super(cardNumber);
    }
    
    @Override
    public void processPayment(double amount) {
        if (validate()) {
            System.out.printf("Processing $%.2f via credit card %s\n", 
                            amount, cardNumber.substring(12));
        }
    }
}

class PayPalPayment implements PaymentMethod {
    private String email;
    
    public PayPalPayment(String email) {
        this.email = email;
    }
    
    @Override
    public boolean validate() {
        return email != null && email.contains("@");
    }
    
    @Override
    public void processPayment(double amount) {
        if (validate()) {
            System.out.printf("Processing $%.2f via PayPal to %s\n", 
                            amount, email);
        }
    }
}

---

## 🔹 Marker Interfaces
Interfaces with no methods (used to mark classes).

interface Serializable { }  // Example of marker interface

class MyClass implements Serializable {
    // Class implementation
}

---

## 🔹 Functional Interfaces (Java 8+)
Interfaces with exactly one abstract method (for lambdas).

@FunctionalInterface
interface Calculator {
    int operate(int a, int b);
}

// Usage with lambda:
Calculator add = (a, b) -> a + b;
Calculator multiply = (a, b) -> a * b;

System.out.println(add.operate(5, 3));      // 8
System.out.println(multiply.operate(5, 3)); // 15

---

## 🔹 Best Practices
1. Use interfaces for multiple inheritance needs
2. Use abstract classes for code reuse among related classes
3. Prefer interfaces for APIs
4. Use @Override annotation consistently
5. Follow interface segregation principle (small, focused interfaces)

---

### 📌 What's Next?
In Part 7, we'll cover:
➡️ Packages
➡️ Access Modifiers
➡️ Encapsulation Deep Dive

#JavaInterfaces #AbstractClasses #OOPConcepts 🚀

# 📚 Java Programming Language – Part 7/10: Packages & Access Modifiers
#Java #Packages #AccessModifiers #Encapsulation

Welcome to Part 7 of our Java series! Today we'll explore how to organize code using packages and control visibility with access modifiers.

---

## 🔹 Packages in Java
Packages help organize classes and prevent naming conflicts.

### 1. Creating and Using Packages

// File: com/example/utils/MathHelper.java
package com.example.utils;  // Package declaration

public class MathHelper {
    public static int add(int a, int b) {
        return a + b;
    }
}

// File: MainApp.java
import com.example.utils.MathHelper;

public class MainApp {
    public static void main(String[] args) {
        int sum = MathHelper.add(5, 3);
        System.out.println("Sum: " + sum);
    }
}

### 2. Common Java Packages
| Package | Contents |
|---------|----------|
| java.lang | Core classes (auto-imported) |
| java.util | Collections, date/time |
| java.io | Input/output operations |
| java.net | Networking |

---

## 🔹 Access Modifiers
Control visibility of classes, methods, and variables.

### 1. Access Levels Overview
| Modifier | Class | Package | Subclass | World |
|----------|-------|---------|----------|-------|
| public | ✅ | ✅ | ✅ | ✅ |
| protected | ✅ | ✅ | ✅ | ❌ |
| default (no modifier) | ✅ | ✅ | ❌ | ❌ |
| private | ✅ | ❌ | ❌ | ❌ |

### 2. Practical Examples

public class BankAccount {
    private double balance;  // Only accessible within class
    
    public String accountNumber;  // Accessible everywhere
    
    protected String ownerName;  // Accessible in package and subclasses
    
    void displayBalance() {  // Package-private (default)
        System.out.println("Balance: " + balance);
    }
}

---

## 🔹 Encapsulation Deep Dive
Proper encapsulation = private fields + public methods.

### 1. Proper Encapsulation Example

public class Student {
    private String id;
    private String name;
    private double gpa;
    
    // Constructor
    public Student(String id, String name) {
        this.id = id;
        this.name = name;
    }
    
    // Getter methods
    public String getId() { return id; }
    public String getName() { return name; }
    public double getGpa() { return gpa; }
    
    // Setter methods with validation
    public void setName(String name) {
        if (name != null && !name.isEmpty()) {
            this.name = name;
        }
    }
    
    public void updateGpa(double newGpa) {
        if (newGpa >= 0 && newGpa <= 4.0) {
            this.gpa = newGpa;
        }
    }
}

### 2. Benefits of Encapsulation
✔️ Better control over data
✔️ Validation in setters
✔️ Hiding implementation details
✔️ Easier to modify internal representation

---

## 🔹 Static Import
Import static members directly.

import static java.lang.Math.PI;
import static java.lang.Math.pow;

public class Circle {
    public static double calculateArea(double radius) {
        return PI * pow(radius, 2);
    }
}

---

## 🔹 Practical Example: Library Management

package com.library.models;

public class Book {
    private String isbn;
    private String title;
    private String author;
    private boolean isAvailable;
    
    public Book(String isbn, String title, String author) {
        this.isbn = isbn;
        this.title = title;
        this.author = author;
        this.isAvailable = true;
    }
    
    // Getters and setters
    public String getIsbn() { return isbn; }
    public String getTitle() { return title; }
    public boolean isAvailable() { return isAvailable; }
    
    public void setAvailable(boolean available) {
        isAvailable = available;
    }
}

package com.library.system;

import com.library.models.Book;

public class Library {
    public void borrowBook(Book book) {
        if (book.isAvailable()) {
            book.setAvailable(false);
            System.out.println("Book borrowed: " + book.getTitle());
        } else {
            System.out.println("Book not available");
        }
    }
}

---

# 📚 Java Programming Language – Part 8/10: Exception Handling
#Java #Exceptions #ErrorHandling #Programming

Welcome to Part 8 of our Java series! Today we'll master how to handle errors and exceptional situations in Java programs.

---

## 🔹 What are Exceptions?
Exceptions are events that disrupt normal program flow:
- Checked Exceptions (Compile-time) - Must be handled
- Unchecked Exceptions (Runtime) - Optional handling
- Errors (Serious problems) - Usually unrecoverable

---

## 🔹 Exception Hierarchy

Throwable
├── Error (e.g., OutOfMemoryError)
└── Exception
    ├── RuntimeException (Unchecked)
    │   ├── NullPointerException
    │   ├── ArrayIndexOutOfBoundsException
    │   └── ArithmeticException
    └── Other Exceptions (Checked)
        ├── IOException
        └── SQLException

---

## 🔹 Try-Catch Block
Basic exception handling structure:

try {
    // Risky code
    int result = 10 / 0;
} catch (ArithmeticException e) {
    // Handle specific exception
    System.out.println("Cannot divide by zero!");
} catch (Exception e) {
    // Generic exception handler
    System.out.println("Something went wrong: " + e.getMessage());
} finally {
    // Always executes (cleanup code)
    System.out.println("Cleanup completed");
}

---

## 🔹 Checked vs Unchecked Exceptions

| Feature | Checked Exceptions | Unchecked Exceptions |
|-----------------|----------------------------|----------------------------|
| Handling | Mandatory (compile error) | Optional |
| Inheritance | Extend Exception | Extend RuntimeException |
| When to Use | Recoverable situations | Programming errors |
| Examples | IOException, SQLException | NullPointerException, ArithmeticException |

---

## 🔹 Throwing Exceptions
### 1. Throw Keyword

public void withdraw(double amount) throws InsufficientFundsException {
    if (amount > balance) {
        throw new InsufficientFundsException("Not enough balance");
    }
    balance -= amount;
}

### 2. Throws Clause

public void readFile() throws IOException {
    FileReader file = new FileReader("data.txt");
    // File operations
}

---

## 🔹 Custom Exceptions
Create your own exception classes:

// Custom checked exception
public class InvalidAgeException extends Exception {
    public InvalidAgeException(String message) {
        super(message);
    }
}

// Custom unchecked exception
public class PaymentFailedException extends RuntimeException {
    public PaymentFailedException(String message) {
        super(message);
    }
}

---

## 🔹 Try-With-Resources
Automatic resource management (Java 7+):

try (FileInputStream fis = new FileInputStream("file.txt");
     BufferedReader br = new BufferedReader(new InputStreamReader(fis))) {
    // Auto-closed after try block
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
} catch (IOException e) {
    e.printStackTrace();
}

---

## 🔹 Practical Example: Bank Transactions

public class BankAccount {
    private double balance;
    
    public void deposit(double amount) throws InvalidAmountException {
        if (amount <= 0) {
            throw new InvalidAmountException("Deposit amount must be positive");
        }
        balance += amount;
    }
    
    public void withdraw(double amount) 
            throws InsufficientFundsException, InvalidAmountException {
        if (amount <= 0) {
            throw new InvalidAmountException("Withdrawal amount must be positive");
        }
        if (amount > balance) {
            throw new InsufficientFundsException("Not enough funds");
        }
        balance -= amount;
    }
}

// Usage:
BankAccount account = new BankAccount();
try {
    account.deposit(1000);
    account.withdraw(500);
    account.withdraw(600);  // Throws exception
} catch (InvalidAmountException | InsufficientFundsException e) {
    System.err.println("Transaction failed: " + e.getMessage());
}

---

# 📚 Java Programming Language – Part 9/10: Collections Framework
#Java #Collections #DataStructures #Programming

Welcome to Part 9 of our Java series! Today we'll explore the powerful Collections Framework - essential for handling groups of objects efficiently.

---

## 🔹 Collections Framework Overview
The Java Collections Framework provides:
- Interfaces (List, Set, Map, etc.)
- Implementations (ArrayList, HashSet, HashMap, etc.)
- Algorithms (Searching, Sorting, Shuffling)


---

## 🔹 Core Interfaces
| Interface | Description | Key Implementations |
|-----------|-------------|---------------------|
| List | Ordered collection (allows duplicates) | ArrayList, LinkedList |
| Set | Unique elements (no duplicates) | HashSet, TreeSet |
| Queue | FIFO ordering | LinkedList, PriorityQueue |
| Map | Key-value pairs | HashMap, TreeMap |

---

## 🔹 List Implementations
### 1. ArrayList

List<String> names = new ArrayList<>();
names.add("Alice");
names.add("Bob");
names.add(1, "Charlie"); // Insert at index 1

System.out.println(names); // [Alice, Charlie, Bob]
System.out.println(names.get(0)); // Alice

### 2. LinkedList

List<Integer> numbers = new LinkedList<>();
numbers.add(10);
numbers.addFirst(5); // Add to beginning
numbers.addLast(20); // Add to end

System.out.println(numbers); // [5, 10, 20]

---

## 🔹 Set Implementations
### 1. HashSet (Unordered)

Set<String> uniqueNames = new HashSet<>();
uniqueNames.add("Alice");
uniqueNames.add("Bob");
uniqueNames.add("Alice"); // Duplicate ignored

System.out.println(uniqueNames); // [Alice, Bob] (order may vary)

### 2. TreeSet (Sorted)

Set<Integer> sortedNumbers = new TreeSet<>();
sortedNumbers.add(5);
sortedNumbers.add(2);
sortedNumbers.add(8);

System.out.println(sortedNumbers); // [2, 5, 8]

---

## 🔹 Map Implementations
### 1. HashMap

Map<String, Integer> ageMap = new HashMap<>();
ageMap.put("Alice", 25);
ageMap.put("Bob", 30);
ageMap.put("Alice", 26); // Overwrites previous value

System.out.println(ageMap.get("Alice")); // 26
System.out.println(ageMap.containsKey("Bob")); // true

### 2. TreeMap (Sorted by keys)

Map<String, String> sortedMap = new TreeMap<>();
sortedMap.put("Orange", "Fruit");
sortedMap.put("Carrot", "Vegetable");
sortedMap.put("Apple", "Fruit");

System.out.println(sortedMap); 
// {Apple=Fruit, Carrot=Vegetable, Orange=Fruit}

---

## 🔹 Iterating Collections
### 1. For-Each Loop

List<String> colors = List.of("Red", "Green", "Blue");
for (String color : colors) {
    System.out.println(color);
}

### 2. Iterator

Set<Integer> numbers = new HashSet<>(Set.of(1, 2, 3));
Iterator<Integer> it = numbers.iterator();
while (it.hasNext()) {
    System.out.println(it.next());
}

### 3. forEach() Method (Java 8+)

Map<String, Integer> map = Map.of("A", 1, "B", 2);
map.forEach((key, value) -> 
    System.out.println(key + ": " + value));

---

## 🔹 Collections Utility Class
Powerful static methods for collections:

List<Integer> numbers = new ArrayList<>(List.of(3, 1, 4, 1, 5));

Collections.sort(numbers); // [1, 1, 3, 4, 5]
Collections.reverse(numbers); // [5, 4, 3, 1, 1]
Collections.shuffle(numbers); // Random order
Collections.frequency(numbers, 1); // 2

---

# 📚 Java Programming Language – Part 10/10: Streams & Modern Java Features
#Java #Streams #Lambda #ModernJava #Programming

Welcome to the final part of our Java series! Today we'll explore powerful modern Java features including Streams API and Lambda expressions.

---

## 🔹 Lambda Expressions
Concise way to implement functional interfaces.

### 1. Basic Syntax

// Traditional way
Runnable r1 = new Runnable() {
    public void run() {
        System.out.println("Running!");
    }
};

// Lambda equivalent
Runnable r2 = () -> System.out.println("Running!");

### 2. Lambda Variations

// No parameters
() -> System.out.println("Hello")

// Single parameter
name -> System.out.println("Hello " + name)

// Multiple parameters
(a, b) -> a + b

// With return and body
(x, y) -> {
    int sum = x + y;
    return sum * 2;
}

---

## 🔹 Functional Interfaces
Single abstract method interfaces work with lambdas.

### 1. Common Functional Interfaces
| Interface | Method | Example Use |
|----------------|----------------|---------------------------|
| Predicate<T> | test(T t) | Filter elements |
| Function<T,R>| apply(T t) | Transform elements |
| Consumer<T> | accept(T t) | Perform actions |
| Supplier<T> | get() | Generate values |

### 2. Practical Example

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");

// Using Predicate
Predicate<String> startsWithA = name -> name.startsWith("A");
names.stream().filter(startsWithA).forEach(System.out::println);

// Using Function
Function<String, Integer> nameLength = String::length;
names.stream().map(nameLength).forEach(System.out::println);

---

## 🔹 Streams API
Powerful way to process collections functionally.

### 1. Stream Pipeline

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

int sum = numbers.stream()          // Source
    .filter(n -> n % 2 == 0)       // Intermediate operation
    .map(n -> n * 2)               // Intermediate operation
    .reduce(0, Integer::sum);      // Terminal operation

System.out.println(sum);  // 12 (2*2 + 4*2)

### 2. Common Stream Operations
| Operation | Type | Example |
|-----------|------|---------|
| filter | Intermediate | .filter(n -> n > 5) |
| map | Intermediate | .map(String::toUpperCase) |
| sorted | Intermediate | .sorted(Comparator.reverseOrder()) |
| forEach | Terminal | .forEach(System.out::println) |
| collect | Terminal | .collect(Collectors.toList()) |
| reduce | Terminal | .reduce(0, Integer::sum) |

---

## 🔹 Method References
Shortcut for lambda expressions.

### 1. Types of Method References

// Static method
Function<String, Integer> parser = Integer::parseInt;

// Instance method of object
Consumer<String> printer = System.out::println;

// Instance method of class
Function<String, String> upper = String::toUpperCase;

// Constructor
Supplier<List<String>> listSupplier = ArrayList::new;

---

## 🔹 Optional Class
Handle null values safely.

### 1. Basic Usage

Optional<String> name = Optional.ofNullable(getName());

String result = name
    .map(String::toUpperCase)
    .orElse("DEFAULT");

System.out.println(result);

### 2. Practical Example

public class UserService {
    public Optional<User> findUser(String id) {
        // May return null
        return Optional.ofNullable(database.findUser(id));
    }
}

// Usage:
userService.findUser("123")
    .ifPresentOrElse(
        user -> System.out.println("Found: " + user),
        () -> System.out.println("User not found")
    );

---

## 🔹 Modern Java Features (Java 8-17)
### 1. Records (Java 16)

public record Person(String name, int age) {}

// Automatically generates:
// - Constructor
// - Getters
// - equals(), hashCode(), toString()

### 2. Pattern Matching (Java 16)

if (obj instanceof String s) {
    System.out.println(s.length());
}

### 3. Text Blocks (Java 15)

String json = """
    {
        "name": "Alice",
        "age": 25
    }
    """;

# 📚 100 Essential Java Interview Questions
#Java #Interview #Programming #OOP #Collections #Multithreading

---

## 🔹 Core Java (20 Questions)
1. What is JVM, JRE, and JDK?
2. Explain public static void main(String[] args)
3. Difference between == and .equals()?
4. What are Java primitives? List all 8.
5. Explain autoboxing/unboxing
6. What are varargs?
7. Difference between String, StringBuilder, and StringBuffer
8. What are immutable objects? How to create them?
9. Explain final, finally, and finalize
10. What are annotations? Common built-in annotations?
11. Difference between throw and throws
12. What is static keyword?
13. Can we override static methods?
14. What is method overloading vs overriding?
15. What is this and super keywords?
16. Explain pass-by-value in Java
17. What are wrapper classes? Why needed?
18. What is enum? When to use?
19. Difference between instanceof and getClass()
20. What is type casting? Implicit vs explicit

---

## 🔹 OOP Concepts (15 Questions)
21. 4 Pillars of OOP with examples
22. What is abstraction vs encapsulation?
23. Difference between abstract class and interface (Java 8+)
24. Can an interface have constructors?
25. What is polymorphism? Runtime vs compile-time
26. What is method hiding?
27. What is composition vs inheritance?
28. What is the Liskov Substitution Principle?
29. How to achieve multiple inheritance in Java?
30. What is a singleton? Thread-safe implementation
31. What is a factory pattern?
32. What is a marker interface?
33. What is a POJO?
34. What is the instanceof operator used for?
35. What is object cloning? Shallow vs deep copy

---

## 🔹 Collections Framework (15 Questions)
36. Collections hierarchy diagram explanation
37. Difference between List, Set, and Map
38. ArrayList vs LinkedList
39. HashSet vs TreeSet
40. HashMap vs HashTable vs ConcurrentHashMap
41. How HashMap works internally?
42. What is hashing? Hashcode/equals contract
43. What is Comparable vs Comparator?
44. Fail-fast vs fail-safe iterators
45. How to make collections immutable?
46. What is PriorityQueue?
47. Difference between Iterator and ListIterator
48. What are Java 8 stream APIs?
49. map() vs flatMap()
50. What are collectors? Common collectors

---

## 🔹 Exception Handling (10 Questions)
51. Exception hierarchy in Java
52. Checked vs unchecked exceptions
53. What is try-with-resources?
54. Can we have try without catch?
55. What is exception propagation?
56. Difference between throw and throws
57. How to create custom exceptions?
58. What is Error vs Exception?
59. Best practices for exception handling
60. What is @SuppressWarnings?

---

## 🔹 Multithreading (15 Questions)
61. Process vs thread
62. Ways to create threads
63. Runnable vs Callable
64. Thread lifecycle states
65. What is synchronization?
66. synchronized keyword usage
67. What are volatile variables?
68. What is deadlock? How to avoid?
69. What is thread starvation?
70. wait(), notify(), notifyAll() methods
71. What is thread pool? Executor framework
72. What is Future and CompletableFuture?
73. What is atomic variable?
74. What is ThreadLocal?
75. Concurrent collections in Java

---

## 🔹 Java 8+ Features (10 Questions)
76. What are lambda expressions?
77. Functional interfaces in Java
78. Method references types
79. Optional class purpose
80. Stream API operations
81. map() vs flatMap()
82. What are default methods?
83. What are static methods in interfaces?
84. New Date/Time API benefits
85. Records and sealed classes

---

## 🔹 JVM & Performance (10 Questions)
86. JVM architecture overview
87. What is classloader?
88. What is bytecode?
89. What is JIT compiler?
90. Heap memory structure
91. What is garbage collection? Types of GC
92. String pool concept
93. How to handle memory leaks?
94. What is OutOfMemoryError? Common causes
95. JVM tuning parameters

---

## 🔹 Advanced Topics (5 Questions)
96. What is reflection? Use cases
97. What are Java modules?
98. What is serialization? How to customize?
99. What are Java generics? Type erasure
100. What is the module system in Java 9?

---

### 📌 Bonus Tips for Interviews
✔️ Always explain with code examples
✔️ Mention real-world applications
✔️ Compare alternatives (e.g., ArrayList vs LinkedList)
✔️ Discuss performance implications
✔️ Be honest about what you don't know

#JavaInterview #CodingInterview #TechPrep 🚀

Practice these well and you'll ace any Java interview!

# 📚 JavaScript Tutorial - Part 1/10: The Complete Beginner's Guide
#JavaScript #WebDev #Programming #BeginnerFriendly

Welcome to Part 1 of our comprehensive 10-part JavaScript series! This tutorial is designed for absolute beginners with detailed explanations and practical examples.

---

## 🔹 What is JavaScript?
JavaScript is a high-level, interpreted programming language that:
- Runs in web browsers (client-side)
- Can also run on servers (Node.js)
- Adds interactivity to websites
- Works with HTML/CSS to create dynamic web pages

Key Features:
✔️ Event-driven programming
✔️ Supports object-oriented and functional styles
✔️ Dynamically typed
✔️ Asynchronous operations (callbacks, promises)

---

## 🔹 JavaScript vs Other Languages
| Feature | JavaScript | Python | Java |
|---------------|---------------|---------------|---------------|
| Typing | Dynamic | Dynamic | Static |
| Execution | Interpreted | Interpreted | Compiled |
| Platform | Browser/Server| Multi-purpose | JVM |
| Paradigms | Multi-paradigm| Multi-paradigm| OOP |

---

## 🔹 How JavaScript Runs?
1. Browser loads HTML/CSS
2. JavaScript engine (V8, SpiderMonkey) executes JS code
3. Can manipulate DOM (Document Object Model)
4. Handles user interactions

HTML → Browser → JavaScript Engine → Execution

---

## 🔹 Setting Up JavaScript
### 1. In HTML File (Most Common)

<script>
  // Your JavaScript code here
  alert("Hello World!");
</script>

<!-- OR External File -->
<script src="script.js"></script>

### 2. Browser Console
- Press F12 → Console tab
- Type JS commands directly

### 3. Node.js (Server-Side)

node filename.js

---

## 🔹 Your First JavaScript Program

// Single line comment
/* Multi-line 
   comment */

// Print to console
console.log("Hello World!"); 

// Alert popup
alert("Welcome to JavaScript!");

// HTML output
document.write("<h1>Hello from JS!</h1>");

---

## 🔹 Variables & Data Types
JavaScript has 3 ways to declare variables:

### 1. Variable Declaration

let age = 25;        // Mutable (block-scoped)
const PI = 3.14;     // Immutable 
var name = "Ali";    // Old way (function-scoped)

### 2. Data Types
| Type | Example | Description |
|-------------|--------------------------|--------------------------|
| Number | 42, 3.14 | All numbers |
| String | "Hello", 'World' | Text data |
| Boolean | true, false | Logical values |
| Object | {name: "Ali", age: 25} | Key-value pairs |
| Array | [1, 2, 3] | Ordered lists |
| Null | null | Intentional empty value |
| Undefined | undefined | Uninitialized variable |

### 3. Type Checking

typeof "Hello";    // "string"
typeof 42;         // "number"
typeof true;       // "boolean"
typeof {};         // "object"

---

## 🔹 Operators
### 1. Arithmetic

let x = 10, y = 3;
console.log(x + y);  // 13
console.log(x - y);  // 7
console.log(x * y);  // 30
console.log(x / y);  // 3.333...
console.log(x % y);  // 1 (modulus)

### 2. Comparison

console.log(5 == "5");   // true (loose equality)
console.log(5 === "5");  // false (strict equality)
console.log(5 != "5");   // false
console.log(5 !== "5");  // true

### 3. Logical

true && false;    // AND → false
true || false;    // OR → true
!true;            // NOT → false

---

## 🔹 Type Conversion
### 1. Explicit Conversion

String(123);        // "123"
Number("3.14");     // 3.14
Boolean(1);         // true

### 2. Implicit Conversion

"5" + 2;      // "52" (string concatenation)
"5" - 2;      // 3 (numeric operation)

---

## 🔹 Practical Example: Simple Calculator

<script>
  let num1 = parseFloat(prompt("Enter first number:"));
  let num2 = parseFloat(prompt("Enter second number:"));
  
  console.log(`Addition: ${num1 + num2}`);
  console.log(`Subtraction: ${num1 - num2}`);
  console.log(`Multiplication: ${num1 * num2}`);
  console.log(`Division: ${num1 / num2}`);
</script>

---

## 🔹 Best Practices for Beginners
1. Use `const` by default, let when needed, avoid var
2. Always declare variables before use
3. Use strict equality (`===`) instead of ==
4. Name variables meaningfully (e.g., userAge not x)
5. Comment your code for complex logic

---

### 📌 What's Next?
In Part 2, we'll cover:
➡️ Conditionals (if/else, switch)
➡️ Loops (for, while)
➡️ Functions

#LearnJavaScript #CodingBasics #WebDevelopment 🚀

Practice Exercise:
1. Create variables for your name, age, and country
2. Calculate the area of a circle (PI * r²)
3. Try different type conversions