If fundamentals are weak, compensation ceiling stays low.

Concepts:

• Variables, data types, operators
• Control flow (if, switch, loops)
• Functions/methods
• Recursion
• Time and space complexity basics (Big-O)
• Memory model basics (stack vs heap)

Deliverable:

• 30–40 basic programs
• Solve 100 beginner problems (arrays, loops, patterns)

Master language internals, not syntax.

• Classes and objects
• Encapsulation
• Inheritance
• Polymorphism
• Abstraction
• Composition vs Inheritance
• Immutable objects
• equals() and hashCode() contract
• toString() best practices

• Heap vs Stack
• ClassLoader
• Garbage Collection (G1, CMS overview)
• String Pool
• Wrapper classes
• Autoboxing pitfalls

• List (ArrayList vs LinkedList)
• Set (HashSet vs TreeSet)
• Map (HashMap vs ConcurrentHashMap)
• Internal working of HashMap (very important)
• Comparable vs Comparator

• Checked vs Unchecked
• Custom exceptions
• Try-with-resources

• Lambda expressions
• Functional interfaces
• Streams (map, filter, reduce, collectors)
• Optional
• Method references
• Date-Time API

• Thread lifecycle
• Synchronization
• volatile
• ExecutorService
• CompletableFuture
• Concurrent collections
• Deadlock, race condition

Deliverables:

• Implement your own mini HashMap
• Build a multithreaded file processor
• Write stream-heavy data transformation project

High-paying jobs test this heavily.

• Arrays, Strings
• Recursion, Backtracking
• Linked List
• Stack, Queue
• Trees (BST, traversals)
• Heap / PriorityQueue
• Hashing
• Graph basics
• Sorting algorithms
• Binary search (very important)

• LeetCode
• GeeksforGeeks
• CodeStudio

Target:

• 250–400 quality problems
• Medium-level confidence
• Solve within 30–40 minutes

This is where salary differentiates.

• Spring Framework Core
• Spring Boot
• REST APIs
• Exception handling
• Validation
• DTO pattern
• Profiles
• Logging (SLF4J)

• SQL (joins, indexing, normalization)
• Transactions
• ACID properties
• JDBC basics
• Spring Data JPA
• Query optimization

Database to learn:

• MySQL or PostgreSQL

• Spring Security
• JWT
• OAuth basics

• Maven
• Gradle

• Swagger / OpenAPI

Deliverables:

• User management system (CRUD + auth)
• E-commerce backend
• Banking transaction simulator

Deploy on:

• Amazon Web Services
• Render
• Railway

• SOLID principles
• Design patterns (Factory, Singleton, Strategy, Observer)
• UML diagrams

• Load balancing
• Caching (Redis basics)
• Microservices vs Monolith
• CAP theorem
• Scalability
• Rate limiting

Study case designs:

• URL Shortener
• Chat System
• Payment Gateway

• Git (branching, rebase, merge conflicts)
• CI/CD basics
• Docker
• Basic Kubernetes understanding

High-paying job requires:

• 2–3 production-grade backend projects
• Clean GitHub profile
• Deployed live links
• Metrics (e.g., "Reduced query time by 40% using indexing")

• DSA heavy
• System design
• Concurrency
• JVM internals

• Spring Boot
• SQL
• API design
• Practical debugging

Focus: Strong fundamentals

Target: Junior backend role

Focus:

• Distributed systems
• Performance tuning
• Deep Spring internals

Focus:

• Architecture
• Cloud-native systems
• Team ownership

• Core Java: 2 months
• DSA: 3 months
• Spring Boot + DB: 2 months
• Projects + Interview prep: 2 months

Total: 8–9 months serious preparation.

• Concurrency expertise
• JVM tuning
• System design
• Cloud architecture
• Performance optimization