Java 8 Streams 75 Days Coding Challenge 🚀

📌 About This Repository

This repository contains my structured practice of Java 8 Stream API coding problems. I am solving 5 problems daily to strengthen my Java backend development skills and improve problem-solving ability for product-based and service-based company interviews.

🎯 Challenge Details

Challenge	Details
Total Problems	75
Daily Goal	5 Problems
Duration	15 Days
Focus	Java Streams + Collections
Purpose	Interview Preparation
Difficulty	Beginner → Intermediate → Advanced

📅 Progress Tracker

Day	Problems	Status
Day 1	1–5	✅ Completed
Day 2	6–10	✅ Completed
Day 3	11–15	✅ Completed
Day 4	16–20	✅ Completed
Day 5	21–25	✅ Completed
Day 6	26–30	✅ Completed
Day 7	31–35	✅ Completed
Day 8	36–40	✅ Completed
Day 9	41–45	🔄 In Progress
Day 10	46–50	⏳ Pending
Day 11	51–55	⏳ Pending
Day 12	56–60	⏳ Pending
Day 13	61–65	⏳ Pending
Day 14	66–70	⏳ Pending
Day 15	71–75	⏳ Pending

🧠 Skills Practiced

• Stream API
• Lambda Expressions
• Functional Interfaces
• Method References
• Optional API
• Collections Processing
• Data Transformations
• Clean Code Practices
• Interview Problem-Solving

📚 Topics Covered

Stream Operations

• filter()
• map()
• flatMap()
• reduce()
• distinct()
• sorted()
• limit()
• skip()

Collectors

• toList()
• toSet()
• toMap()
• groupingBy()
• partitioningBy()
• counting()
• joining()

Real World Scenarios

• Employee object processing
• Salary sorting
• Department grouping
• Duplicate detection
• Data transformation
• Analytics style problems

📂 Project Structure

Java8-Streams-75-Challenge
│
├── Day01_Basics
├── Day02_Filter_Map
├── Day03_Sorting
├── Day04_Distinct
├── Day05_Reduce
├── Day06_Collectors
├── Day07_Grouping
├── Day08_Optional
├── Day09_CustomObjects
├── Day10_AdvancedStreams
├── Day11_Practice
├── Day12_Practice
├── Day13_Practice
├── Day14_Practice
├── Day15_FinalPractice
│
└── README.md

💡 Sample Problem

Find Even Numbers using Streams

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class LazyDeveloper1
{
    static void main(String[] args)
    {
        List<String> words=Arrays.asList("a","e","i","o","u","Jee",
                "Jeevan","2025Champions","NammaRcb","Kohli");
        List<String> result= words.stream()
                .filter(s->s.length()>3)
                .map(String::toUpperCase)
                .collect(Collectors.toList());
        System.out.println(result);
    }
}

🚀 Learning Outcome

By completing this challenge I aim to:

• Master Java Stream API
• Improve coding consistency
• Write optimized Java code
• Gain confidence for backend interviews
• Improve problem-solving speed

🎯 Interview Preparation Focus

This repository helps prepare for:

• Java Backend Developer roles
• Spring Boot Developer roles
• Product company interviews
• Startup hiring rounds
• Service company interviews

🔥 Motivation

Daily consistency is the main focus of this challenge.

5 Problems Daily = Strong Java Stream Skills

🤝 Contribution

Suggestions and improvements are welcome.

⭐ Support

If this repository helps you, consider giving a star.

👨‍💻 Author

Java Backend Developer

• Java
• Spring Boot
• SQL
• Microservices
• DSA
• Java Streams

📬 Connect

Feel free to raise an issue for discussion or improvements.

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Code • Practice • Improve • Repeat