Java is one of the most versatile and widely-used programming languages, powering everything from large-scale enterprise systems to Android apps. For those looking to build a career in software development, mastering Java is an essential step. Whether you're a fresher, a beginner, or a developer seeking to enhance your skills, this 100-day roadmap will guide you through a structured learning path, starting from the basics and leading you to advanced Java concepts. By following this plan, you’ll not only gain theoretical knowledge but also practical experience through hands-on projects.

Phase 1: Days 1–30 (Beginner: Core Java Fundamentals)

Week 1 (Days 1-7): Setting the Foundation

Your Java journey begins by laying a solid foundation. During the first week, familiarize yourself with the history of Java, its widespread applications, and how to set up the Java Development Kit (JDK) along with popular Integrated Development Environments (IDEs) like IntelliJ IDEA or Eclipse.

Key Concepts:

• Data Types and Variables
• Operators and Expressions
• Control Structures (if-else, switch-case)
• Loops (for, while, do-while)

Mini Project: Develop a simple calculator or temperature converter to apply these basic concepts.

Week 2 (Days 8-14): Object-Oriented Programming (OOP) Basics

OOP is the core of Java, and this week introduces you to its fundamental principles. Learn how to create classes and objects, and understand key OOP concepts such as inheritance, polymorphism, encapsulation, and abstraction.

Key Concepts:

• Classes and Objects
• Methods and Constructors
• OOP Principles (Inheritance, Polymorphism, Encapsulation, and Abstraction)

Hands-on Practice: Create a Bank Account Management System using OOP concepts to get a practical grasp of these principles.

 

Week 3 (Days 15-21): Arrays and Strings

Array manipulation and string handling are critical in Java programming. During this week, you'll delve into arrays and learn how Java manages strings through the String class, StringBuilder, and StringBuffer.

Key Concepts:

• Arrays: One-dimensional and Multi-dimensional Arrays
• String Class Methods
• StringBuilder and StringBuffer

Mini Project: Build a Library Management System using arrays and string manipulation techniques.

Week 4 (Days 22-30): Exception Handling and File Handling

Effective error handling and file manipulation are essential for robust Java applications. This week, explore exception handling mechanisms and dive into file input/output (I/O) operations.

Key Concepts:

• Try, Catch, and Finally Blocks
• Custom Exceptions
• File I/O (reading and writing files)

Mini Project: Create a File Organizer Tool that sorts and manages files based on user input.

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Phase 2: Days 31–70 (Intermediate: Core to Advanced Concepts)

 

Week 5 (Days 31-37): Collections Framework

Java’s Collections Framework is a powerful tool for handling groups of objects. This week, familiarize yourself with lists, sets, and maps, and how to use popular implementations like ArrayList, HashSet, and HashMap.

Key Concepts:

• List, Set, and Map Interfaces
• ArrayList, LinkedList, HashSet, and HashMap
• Iterators and Enhanced For Loop

Mini Project: Develop a Student Management System using Java Collections for efficient data storage and retrieval.

Week 6 (Days 38-44): Generics, Lambda Expressions, and Stream API

Generics and lambdas simplify data handling and functional programming in Java. This week focuses on these advanced concepts and the Stream API for processing data in a more efficient, declarative way.

Key Concepts:

• Generics and Wildcards
• Lambda Expressions for Functional Programming
• Streams: Filter and Map Operations

Mini Project: Implement a Data Filtering Application using Streams and Lambda Expressions.

Week 7 (Days 45-51): Multithreading and Concurrency

Multithreading is a core concept for writing concurrent programs in Java. This week, explore how to create and manage threads and handle concurrency challenges.

Key Concepts:

• Thread Lifecycle and Synchronization
• Executors, Future, and Callable Interfaces
• Concurrency Utilities (Locks, Semaphore)

Mini Project: Build a Multithreaded File Downloader that allows simultaneous downloads, improving efficiency.

Week 8 (Days 52-58): Java I/O and Serialization

Java provides robust mechanisms for reading and writing data to files. In this week, focus on Java I/O streams, readers and writers, and the process of serialization.

Key Concepts:

• InputStream and OutputStream
• Readers and Writers
• Serialization and Deserialization

Mini Project: Create a File Compression Utility using Java I/O and serialization.

Week 9 (Days 59-65): JDBC and Database Connectivity

This week is all about connecting Java applications to databases using Java Database Connectivity (JDBC). You’ll learn how to perform CRUD operations on a database like MySQL.

Key Concepts:

• JDBC Basics
• Connecting to a Database
• Performing CRUD Operations (Create, Read, Update, Delete)

Mini Project: Build an Employee Management System with database integration.

Week 10 (Days 66-70): Introduction to Design Patterns

Design patterns offer best practices for solving common software design problems. This week covers essential design patterns that every Java developer should know.

Key Concepts:

• Singleton, Factory, Observer, and Decorator Patterns
• Importance of Design Patterns

Mini Project: Implement the Factory Pattern in a Shape Drawing Application.

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Phase 3: Days 71–100 (Advanced Java Concepts and Frameworks)

Week 11 (Days 71-77): Java Servlets and JSP

Transition into web development with Java, focusing on building dynamic web applications using Java Servlets and JavaServer Pages (JSP).

Key Concepts:

• Servlet Lifecycle
• Handling HTTP Requests and Responses
• JSP Tags and Scripting Elements

Mini Project: Develop a To-Do List App using Servlets and JSP.

Week 12 (Days 78-84): Spring Framework Basics

Spring is one of the most popular Java frameworks. This week introduces the fundamentals of Spring, including Dependency Injection and building RESTful web services.

Key Concepts:

• Spring Framework Overview
• Dependency Injection and Inversion of Control
• Spring MVC and RESTful Web Services

Mini Project: Build a REST API for an E-commerce Application using Spring.

Week 13 (Days 85-91): Spring Boot and Microservices

Microservices architecture is key to modern software development. Learn how to create microservices using Spring Boot and how to integrate them with databases.

Key Concepts:

• Spring Boot Basics
• Building Microservices
• REST APIs and Database Integration

Mini Project: Develop a Microservices-based E-commerce System.

Week 14 (Days 92-97): Unit Testing with JUnit and Mockito

This week covers writing unit tests with JUnit and Mockito, preparing you to adopt Test-Driven Development (TDD).

Key Concepts:

• Unit Testing with JUnit
• Mocking Dependencies with Mockito
• Test-Driven Development (TDD)

Mini Project: Write unit tests for the REST API of an Inventory Management System.

Week 15 (Days 98-100): Version Control with Git and Final Project

Version control is essential for collaborative software development. Learn Git basics and set up a final project that combines all the concepts you've learned.

Key Concepts:

• Introduction to Git and GitHub
• Basic Git Commands
• Collaborating on GitHub

Final Project: Develop a full-stack web application that includes Servlets, Spring, JDBC, and REST APIs.

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Conclusion: 100 Days to Java Mastery

By the end of this 100-day roadmap, you will have gained both the theoretical understanding and practical skills needed to master Java. From core programming concepts to advanced frameworks like Spring, this journey equips you to tackle real-world challenges and explore exciting career opportunities as a Java Developer, Software Engineer, or Backend Developer.

The learning doesn’t stop here—continue exploring advanced topics like Spring Cloud, Microservices architecture, and DevOps to stay ahead in the ever-evolving world of Java development.