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Java 8 Streams 75 Days Coding Challenge 🚀

Java Streams Practice Status

📌 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.

Code • Practice • Improve • Repeat