1️⃣ Variables & Data Types
- `int`, `double`, `char`, `boolean`, `String` - `float`, `long`, `short`, `byte`2️⃣ Operators
- Arithmetic, Logical, Relational, Bitwise, Assignment, Unary, Ternary3️⃣ Control Statements
- `if`, `else`, `else if`, `switch`, `case`, `default` - `break`, `continue`, `return`4️⃣ Loops
- `for`, `while`, `do-while` - `for-each` loop (array/list iteration)5️⃣ Classes & Objects
- Class declaration - Object creation using `new` - Constructors (default & parameterized)6️⃣ Methods
- Method declaration & overloading - Return types & parameters - `static` vs instance methods7️⃣ Access Modifiers
- `public`, `private`, `protected`, default (package-private)8️⃣ OOP Concepts
- Inheritance - Polymorphism (compile-time & runtime) - Abstraction (abstract class + interface) - Encapsulation (getters/setters)9️⃣ Arrays & Collections
- Single & multi-dimensional arrays - `ArrayList`, `LinkedList`, `HashSet`, `HashMap` - Iterators & for-each loops🔟 Exception Handling
- `try`, `catch`, `finally`, `throw`, `throws` - Checked vs unchecked exceptions - Custom exceptions1️⃣1️⃣ Strings & StringBuilder
- String immutability & methods - Mutable alternatives: `StringBuilder`, `StringBuffer`1️⃣2️⃣ Java 8+ Features
- Lambda expressions - Streams API - Functional interfaces - `Optional` & method references1️⃣3️⃣ File Handling (I/O)
- `File`, `FileReader`, `FileWriter`, `BufferedReader`, `BufferedWriter` - `Scanner` - Serialization & deserialization1️⃣4️⃣ Multithreading
- `Thread` & `Runnable` - Thread lifecycle & synchronization - Executors framework1️⃣5️⃣ Inner Classes
- Static, non-static, anonymous, local inner classes1️⃣6️⃣ Enums
- Enum declaration, usage, and switch-case1️⃣7️⃣ Generics
- Generic classes & methods - Bounded types & wildcards1️⃣8️⃣ JVM, JRE, JDK
- Compilation & execution flow - Memory: Heap vs Stack - Garbage collection basics1️⃣9️⃣ Annotations
- Built-in: `@Override`, `@Deprecated`, `@SuppressWarnings` - Custom annotations2️⃣0️⃣ Reflections API
- Inspect classes, methods, fields at runtime2️⃣1️⃣ Networking
- `Socket`, `ServerSocket`, URL & HTTP connections2️⃣2️⃣ Design Patterns
- Singleton, Factory, Strategy, Observer, Builder2️⃣3️⃣ Maven/Gradle
- Build automation & dependency management - `pom.xml`, `build.gradle` basics2️⃣4️⃣ JUnit & Testing
- Unit testing, assertions, test suites2️⃣5️⃣ Spring Framework (Bonus)
- Spring Boot basics - Dependency Injection & REST APIs - Annotations & configurations📌 DAY 1 – Core Java & Collections Deep Dive
Topics:
- OOP: Polymorphism, Abstraction, Inheritance, Encapsulation
equals(),hashCode(),toString(), immutability- Collections:
ArrayListvsLinkedList,HashMapinternals,HashSet,TreeSet,LinkedHashMap - Fail-fast vs fail-safe iterators, Comparable vs Comparator
- Java Memory: Stack vs Heap, GC basics
Focus:
- Understand internal mechanics of collections
- Be able to whiteboard custom HashMap / LRU cache
Practice:
- Implement custom
LinkedList - Implement custom
HashMap - Sort a list of custom objects using
Comparator
📌 DAY 2 – Java 8 & Functional Programming
Topics:
- Functional interfaces:
Predicate,Function,Supplier,Consumer - Lambdas: syntax, chaining, performance
- Streams API:
map,filter,reduce,sorted,collect,flatMap,groupingBy,partitioningBy Optionalusage- Default & static methods in interfaces
Focus:
- Refactor imperative code to streams
- Understand intermediate vs terminal operations
- Explain
map()vsflatMap()
Practice:
- Convert loops to Stream API
- Use
Optionalto avoid nulls
📌 DAY 3 – Multithreading & Concurrency
Topics:
- Thread lifecycle,
Thread,Runnable,Callable,Future,Executors - Synchronization:
synchronized,volatile,ReentrantLock wait(),notify(),notifyAll()- Thread-safe structures:
ConcurrentHashMap,CopyOnWriteArrayList - Deadlocks & race conditions
Focus:
- Explain synchronization problems with examples
- Master common concurrency problems: producer-consumer, odd/even printing, reader-writer lock
Practice:
- Implement concurrency problems above
- Rewrite shared counter using
AtomicInteger&ReentrantLock
📌 DAY 4 – Spring & Spring Boot Essentials
Topics:
- Spring Core: IoC, DI, Bean lifecycle, scopes
- Spring Boot:
@SpringBootApplication,@Component,@Configuration,@Bean, Profiles, Auto-configuration - Spring MVC: Controller → Service → Repository
- Spring Data JPA:
CrudRepository,PagingAndSortingRepository, JPQL vs Native Query, DTO mapping - Exception handling & validation
Focus:
- Describe request lifecycle in Spring Boot
- Know 20+ annotations by heart
Practice:
- Build a CRUD module with pagination, custom queries, validation
📌 DAY 5 – System Design & Design Patterns
Topics:
- Low-level design: Layered architecture, DTO/VO, Mapper pattern, caching
- High-level design: Load balancer, DB sharding, rate limiter, queues (RabbitMQ/Kafka)
- Design Patterns: Singleton, Factory, Strategy, Template, Decorator, Observer, Builder
Focus:
- Explain project architecture
- Master 1–2 design patterns per use-case
Practice:
- Design Notification System, URL Shortener, or Order Management Module
📌 DAY 6 – DSA for Java Interviews
Topics:
- Arrays & Strings (2-pointer, sliding window)
- HashMap/Set usage
- Stacks/Queues, Recursion, Backtracking
- Trees & Binary Search, Sorting (merge/quick)
- High-yield problems: LRU Cache, Longest Substring without Repeat, Kth Largest Element, Top K Frequent
Focus:
- Solve 30 high-yield problems deeply
- Focus on brute → optimized approach
Practice:
- LeetCode Easy/Medium: 10–15 selective problems
- Track: Problem | Approach | Complexity | Mistakes
📌 DAY 7 – Mock Interviews & Dry Runs
Topics:
- Collections vs Concurrency: HashMap in multi-threading
- Spring Boot request lifecycle
- Custom project-based design Q&A
- Review 2–3 tough bugs
Practice:
- Mock interview (with ChatGPT or friend)
- Whiteboard 1–2 system design problems
- Prepare “Tell me about this project” walkthrough