# 📚 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

---

# 📚 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>

---

# 📚 JavaScript Tutorial - Part 2/10: Control Flow & Functions
#JavaScript #WebDev #Programming #Beginners

Welcome to Part 2 of our JavaScript series! Today we'll master decision-making and functions - the building blocks of programming logic.

---

## 🔹 Conditional Statements
Control program flow based on conditions.

### 1. if-else Statement

let age = 18;

if (age >= 18) {
    console.log("You're an adult");
} else {
    console.log("You're a minor");
}

### 2. Ternary Operator (Shorthand if-else)

let message = (age >= 18) ? "Adult" : "Minor";
console.log(message);

### 3. switch-case Statement

let day = 3;
let dayName;

switch(day) {
    case 1: dayName = "Monday"; break;
    case 2: dayName = "Tuesday"; break;
    case 3: dayName = "Wednesday"; break;
    default: dayName = "Unknown";
}

console.log(dayName); // "Wednesday"

---

## 🔹 Loops
Execute code repeatedly.

### 1. for Loop

for (let i = 1; i <= 5; i++) {
    console.log(`Count: ${i}`);
}
// Output: 1, 2, 3, 4, 5

### 2. while Loop

let count = 1;
while (count <= 5) {
    console.log(count);
    count++;
}

### 3. do-while Loop

let x = 1;
do {
    console.log(x);
    x++;
} while (x <= 5);

### 4. for...of Loop (Arrays)

const colors = ["red", "green", "blue"];
for (const color of colors) {
    console.log(color);
}

### 5. for...in Loop (Objects)

const person = {name: "Ali", age: 25};
for (const key in person) {
    console.log(`${key}: ${person[key]}`);
}

---

## 🔹 Functions
Reusable blocks of code.

### 1. Function Declaration

function greet(name) {
    return `Hello, ${name}!`;
}
console.log(greet("Ali")); // "Hello, Ali!"

### 2. Function Expression

const square = function(x) {
    return x * x;
};
console.log(square(5)); // 25

### 3. Arrow Functions (ES6+)

const add = (a, b) => a + b;
console.log(add(2, 3)); // 5

### 4. Default Parameters

function createUser(name, role = "user") {
    console.log(`${name} is a ${role}`);
}
createUser("Ali"); // "Ali is a user"

### 5. Rest Parameters

function sum(...numbers) {
    return numbers.reduce((total, num) => total + num, 0);
}
console.log(sum(1, 2, 3)); // 6

---

## 🔹 Practical Example: Grade Calculator

function calculateGrade(score) {
    if (score >= 90) return "A";
    else if (score >= 80) return "B";
    else if (score >= 70) return "C";
    else return "F";
}

const studentScore = 85;
console.log(`Grade: ${calculateGrade(studentScore)}`); // "Grade: B"

---

## 🔹 Scope in JavaScript
### 1. Global Scope

const globalVar = "I'm global";

function test() {
    console.log(globalVar); // Accessible
}

### 2. Function Scope (var)

function test() {
    var functionVar = "I'm function-scoped";
}
console.log(functionVar); // Error: Not accessible

### 3. Block Scope (let/const)

if (true) {
    let blockVar = "I'm block-scoped";
}
console.log(blockVar); // Error: Not accessible

---

## 🔹 Error Handling
### 1. try-catch-finally

try {
    // Risky code
    nonExistentFunction();
} catch (error) {
    console.log("Error occurred:", error.message);
} finally {
    console.log("This always executes");
}

### 2. Throwing Custom Errors

function divide(a, b) {
    if (b === 0) throw new Error("Cannot divide by zero!");
    return a / b;
}

---

## 🔹 Best Practices
1. Use strict equality (===) over ==
2. Prefer const/let over var
3. Keep functions small/single-purpose
4. Always handle errors
5. Use descriptive names for functions/variables

---

### 📌 What's Next?
In Part 3, we'll cover:
➡️ Arrays & Array Methods
➡️ Objects & JSON
➡️ Destructuring

#LearnJavaScript #CodingBasics #WebDevelopment 🚀

Practice Exercise:
1. Create a function to check if a number is even/odd
2. Write a loop that prints prime numbers up to 20
3. Make a temperature converter function (Celsius ↔️ Fahrenheit)

# 📚 JavaScript Tutorial - Part 3/10: Arrays, Objects & JSON
#JavaScript #WebDev #Programming #DataStructures

Welcome to Part 3 of our JavaScript series! Today we'll master arrays, objects, and JSON - essential for handling complex data.

---

## 🔹 Arrays in JavaScript
Ordered collections that can hold multiple values.

### 1. Creating Arrays

// Array literal (recommended)
const fruits = ['Apple', 'Banana', 'Orange'];

// Array constructor
const numbers = new Array(1, 2, 3);

// Mixed data types
const mixed = [1, 'Hello', true, {name: 'Ali'}];

### 2. Accessing Elements

console.log(fruits[0]);  // "Apple" (0-based index)
console.log(fruits.length);  // 3

### 3. Common Array Methods
| Method | Description | Example |
|--------|-------------|---------|
| push() | Add to end | fruits.push('Mango') |
| pop() | Remove from end | fruits.pop() |
| shift() | Remove from start | fruits.shift() |
| unshift() | Add to start | fruits.unshift('Kiwi') |
| slice() | Get sub-array | fruits.slice(1, 3) |
| splice() | Add/remove items | fruits.splice(1, 0, 'Berry') |

---

## 🔹 Modern Array Methods (ES6+)
Powerful functional programming tools.

### 1. forEach()

fruits.forEach(fruit => console.log(fruit));

### 2. map()

const upperFruits = fruits.map(fruit => fruit.toUpperCase());

### 3. filter()

const longFruits = fruits.filter(fruit => fruit.length > 5);

### 4. reduce()

const sum = [1, 2, 3].reduce((total, num) => total + num, 0);

### 5. find() & findIndex()

const banana = fruits.find(fruit => fruit === 'Banana');
const bananaIndex = fruits.findIndex(fruit => fruit === 'Banana');

### 6. some() & every()

const hasApple = fruits.some(fruit => fruit === 'Apple');
const allLong = fruits.every(fruit => fruit.length > 3);

---

## 🔹 Objects in JavaScript
Collections of key-value pairs (properties).

### 1. Creating Objects

// Object literal (recommended)
const person = {
    name: 'Ali',
    age: 25,
    hobbies: ['reading', 'coding'],
    address: {
        city: 'Dubai',
        country: 'UAE'
    }
};

### 2. Accessing Properties

// Dot notation
console.log(person.name);  // "Ali"

// Bracket notation (useful for dynamic keys)
const key = 'age';
console.log(person[key]);  // 25

### 3. Modifying Objects

// Add property
person.job = 'Developer';

// Delete property
delete person.age;

// Check property existence
'name' in person;  // true

---

## 🔹 Object Methods
### 1. Object.keys()

const keys = Object.keys(person);  // ["name", "age", ...]

### 2. Object.values()

const values = Object.values(person);

### 3. Object.entries()

for (const [key, value] of Object.entries(person)) {
    console.log(`${key}: ${value}`);
}

### 4. Object Spread (ES9+)

const newPerson = {...person, age: 26};

---

## 🔹 JSON (JavaScript Object Notation)
Universal data format for APIs.

### 1. JSON ↔️ JavaScript

// Object to JSON string
const jsonStr = JSON.stringify(person);

// JSON string to object
const parsedObj = JSON.parse(jsonStr);

### 2. JSON Structure

{
    "name": "Ali",
    "age": 25,
    "isStudent": false,
    "courses": ["Math", "CS"]
}

---

## 🔹 Destructuring Assignment
Unpack values from arrays/objects.

### 1. Array Destructuring

const [first, second] = fruits;
console.log(first);  // "Apple"

### 2. Object Destructuring

const {name, age} = person;
console.log(name);  // "Ali"

// With renaming
const {name: personName} = person;

### 3. Function Parameter Destructuring

function printUser({name, age}) {
    console.log(`${name} is ${age} years old`);
}

---

## 🔹 Practical Example: Todo List Manager

const todoList = [
    {id: 1, task: 'Buy groceries', completed: false},
    {id: 2, task: 'Do laundry', completed: true}
];

// Add new task
function addTask(task) {
    const newTask = {
        id: todoList.length + 1,
        task,
        completed: false
    };
    todoList.push(newTask);
}

// Mark task as complete
function completeTask(id) {
    const task = todoList.find(item => item.id === id);
    if (task) task.completed = true;
}

// Get pending tasks
function getPendingTasks() {
    return todoList.filter(task => !task.completed);
}

---

## 🔹 Best Practices
1. Use `const` for arrays/objects (the reference is constant)
2. Prefer functional methods (map, filter) over loops
3. Validate JSON before parsing
4. Use descriptive property names
5. Destructure deeply nested objects carefully

---

### 📌 What's Next?
In Part 4, we'll cover:
➡️ DOM Manipulation
➡️ Event Handling
➡️ Form Validation

#JavaScript #WebDevelopment #Programming 🚀

Practice Exercise:
1. Create an array of products (name, price, inStock)
2. Write functions to:
- Filter out-of-stock products
- Calculate total inventory value
- Sort by price (high-to-low)
3. Convert your array to JSON and back

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