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☕ Java Lesson – Functional Programming in Java

Is lesson me hum seekhenge:

  • Functional Programming kya hota hai
  • Imperative vs Functional style
  • Lambda Expressions
  • Functional Interfaces
  • Streams API
  • Real examples

1️⃣ Functional Programming Kya Hota Hai?

Functional Programming ka matlab:

code ko functions ke form me likhna

✔ less code
✔ clean code
✔ readable code

2️⃣ Imperative vs Functional

Imperative (Traditional)

int sum = 0;

for(int i = 1; i <= 5; i++){
    sum += i;
}

Functional

int sum = IntStream.rangeClosed(1,5).sum();

3️⃣ Lambda Expression

Lambda ek short way hai function likhne ka:

(parameters) -> expression

Example:

(a, b) -> a + b

4️⃣ Functional Interface

Functional Interface:

jisme sirf ek abstract method hota hai

Example:

interface MyInterface {
    void display();
}

Lambda use:

MyInterface obj = () -> {
    System.out.println("Hello");
};

5️⃣ Built-in Functional Interfaces

Interface Use
Predicate condition check
Function input → output
Consumer accept value
Supplier value provide

6️⃣ Predicate Example

Predicate<Integer> isEven = n -> n % 2 == 0;

System.out.println(isEven.test(4));

7️⃣ Function Example

Function<Integer, Integer> square = x -> x * x;

System.out.println(square.apply(5));

8️⃣ Consumer Example

Consumer<String> print = s -> System.out.println(s);

print.accept("Hello");

9️⃣ Supplier Example

Supplier<Integer> random = () -> 100;

System.out.println(random.get());

🔟 Streams API

Streams use hota hai:

data processing ke liye (collection par)

1️⃣1️⃣ Stream Example

import java.util.*;

class Test {

    public static void main(String[] args){

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

        list.stream()
            .filter(n -> n % 2 == 0)
            .forEach(System.out::println);
    }
}

1️⃣2️⃣ Map Example

list.stream()
    .map(n -> n * n)
    .forEach(System.out::println);

1️⃣3️⃣ Reduce Example

int sum = list.stream()
              .reduce(0, (a, b) -> a + b);

System.out.println(sum);

1️⃣4️⃣ Method Reference

Short form:

System.out::println

1️⃣5️⃣ Advantages

✔ less code
✔ better readability
✔ parallel processing possible

1️⃣6️⃣ Real-Life Example

filter → even numbers
map → square
reduce → sum

1️⃣7️⃣ Important Points

✔ Java 8 se introduce hua
✔ Lambda + Stream important hai
✔ functional style modern coding hai

🎯 Interview Questions

  1. Functional Programming kya hota hai?
  2. Lambda kya hota hai?
  3. Functional interface kya hota hai?
  4. Stream API ka use kya hai?

🧾 Lesson Summary

Is lesson me humne seekha:

✔ Functional Programming concept
✔ Lambda Expressions
✔ Functional Interfaces
✔ Streams API
✔ Real examples

Functional Programming Java me clean, concise aur powerful coding style provide karta hai.