How to switch from 4 LPA to 20 LPA as Java Developer

If you are working in IT company and stuck at low salary or if you are working in support or non tech domain still you can transition into backend domain very easily within 4 months.

I will Provide detailed step by step curriculum to follow to clear high paying job :

1. Core Java ( 1 Month )
Topics :

1. Java Basics & Syntax Setup

• JVM, JRE, and JDK Architecture
• Data Types (Primitive vs. Non-Primitive) & Variables
• Operators (Arithmetic, Relational, Logical, Bitwise)
• Control Flow Statements (if-else, switch-case, for, while, do-while)
• Arrays (Single & Multi-dimensional)

2. Object-Oriented Programming (OOPs)

• Classes, Objects, & Constructors
• Four Pillars: Encapsulation, Inheritance, Polymorphism, Abstraction
• Method Overloading & Method Overriding
• Access Modifiers (public, protected, private, default)
• Keywords: this, super, static, final, instanceof
• Interfaces & Abstract Classes

3. String Handling & Core Utilities

• String, StringBuilder, and StringBuffer classes
• String Immutability & String Constant Pool
• Wrapper Classes, Autoboxing, and Unboxing

4. Exception Handling

• Exception Hierarchy (Throwable, Exception, Error)
• try, catch, finally, throw, and throws
• Checked vs. Unchecked (Runtime) Exceptions
• Creating Custom Exceptions

5. Java Collections Framework & Generics

• Generics: Type Safety & Wildcards (? extends T, ? super T)
• List Interface: ArrayList, LinkedList, Vector
• Set Interface: HashSet, LinkedHashSet, TreeSet
• Map Interface: HashMap, LinkedHashMap, TreeMap, ConcurrentHashMap
• Queue Interface & Iterators (Iterator, ListIterator)

6. Multithreading & Concurrency

• Thread Lifecycle & Creating Threads (Thread class, Runnable interface)
• Synchronization, Locks, and Deadlocks
• Inter-thread Communication (wait(), notify(), notifyAll())
• Executor Framework & Thread Pools (java.util.concurrent)

7. Modern Java Concepts (Java 8+)

• Lambda Expressions & Functional Interfaces (Predicate, Function, Consumer, Supplier)
• Stream API (Filtering, Mapping, Reducing, Collecting)
• Optional Class for NullPointer prevention
• New Date & Time API (java.time package)

8. Java I/O & Memory Management

• Byte Streams & Character Streams (FileInputStream, BufferedReader, etc.)
• Object Serialization & Deserialization
• Garbage Collection algorithms & Memory Areas (Heap, Stack, Metaspace)

Note: Practice More on Java 8 Stream Questions that asked in every interview. Service based companies mostly asked questions on Java 8 Features, Oops, Collections, Multithreading etc…

2. Spring-Boot (1 Month)
Topics:

1. Core Spring & Setup

• Spring Framework Foundations (IoC Container, Dependency Injection)
• Spring Boot Architecture & Auto-Configuration (@SpringBootApplication)
• pom.xml / build.gradle Configuration & Starter Dependencies
• Application Properties & YAML Configurations (@Value, @ConfigurationProperties)
• Profiles & Environment Management (@Profile)

2. RESTful Web Services & Spring MVC

• Building REST APIs (@RestController, @GetMapping, @PostMapping, @PutMapping, @DeleteMapping)
• Request Handling (@PathVariable, @RequestParam, @RequestBody)
• Response Formatting & ResponseEntity
• Exception Handling (@ControllerAdvice, @ExceptionHandler, Problem Details)
• DTO (Data Transfer Object) Pattern & Request Validation (jakarta.validation)

3. Data Access & Persistence (Spring Data JPA)

• ORM & JPA Basics (Entities, Relationships: @OneToMany, @ManyToMany, etc.)
• Spring Data JPA Repositories (CrudRepository, JpaRepository)
• Derived Query Methods & Custom JPQL/Native Queries (@Query)
• Database Migrations (Flyway or Liquibase)
• Transaction Management (@Transactional)

4. Spring Security

• Authentication vs. Authorization Fundamentals
• Security Filter Chain & Configuration
• UserDetailsService & In-Memory / Database Authentication
• JWT (JSON Web Tokens) & Stateless Authentication
• Role-Based & Permission-Based Access Control (@PreAuthorize)
• OAuth2 & OpenID Connect Integration

5. Microservices & Distributed Systems

• Service Discovery (Eureka / Consul)
• API Gateway (Spring Cloud Gateway)
• Inter-Service Communication (REST Template, WebClient, OpenFeign)
• Circuit Breaker & Resilience (Resilience4j)
• Centralized Configuration (Spring Cloud Config)

6. Testing

• Unit Testing with JUnit 5 & Mockito (@Mock, @InjectMocks)
• Integration Testing with @SpringBootTest
• Testing Web Layer with @WebMvcTest & MockMvc
• Repository Testing with @DataJpaTest & Testcontainers

7. Observability & Production Readiness

• Spring Boot Actuator (Health checks, Metrics, Info endpoints)
• Logging Frameworks (SLF4J, Logback) & Structured Logging
• Distributed Tracing & Metrics (Micrometer, Zipkin/Jaeger, Prometheus, Grafana)
• Dockerization (Containerizing Spring Boot apps) & Kubernetes basics

Note : Companies mostly asked questions on Annotations, Microservice Design Pattern etc..

3. SQL (1 month)
Topics:

1. SQL Basics & Data Definition (DDL)

• Data Types (INT, VARCHAR, DATE, BOOLEAN, DECIMAL, BLOB)
• Relational Database Concepts (Tables, Rows, Columns, Keys)
• Database Schema & Table Creation (CREATE DATABASE, CREATE TABLE)
• Modifying Structure (ALTER TABLE, DROP TABLE, TRUNCATE TABLE)
• Constraints (PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, CHECK, DEFAULT)

2. Data Manipulation (DML) & Basic Querying

• Inserting Data (INSERT INTO)
• Querying Data (SELECT, SELECT DISTINCT)
• Filtering Results (WHERE, AND, OR, NOT, IN, BETWEEN, LIKE, IS NULL)
• Updating & Deleting Records (UPDATE, DELETE)
• Sorting & Limiting (ORDER BY, LIMIT / OFFSET / TOP)

3. Aggregations & Grouping

• Aggregate Functions (COUNT, SUM, AVG, MIN, MAX)
• Grouping Data (GROUP BY)
• Filtering Aggregated Groups (HAVING vs WHERE)
• Aliasing Tables and Columns (AS)

4. Joins & Multi-Table Operations

• INNER JOIN & LEFT (OUTER) JOIN
• RIGHT (OUTER) JOIN & FULL (OUTER) JOIN
• CROSS JOIN & SELF JOIN
• Set Operations (UNION, UNION ALL, INTERSECT, EXCEPT / MINUS)

5. Advanced Querying & Subqueries

• Scalar and Multi-row Subqueries
• Correlated Subqueries
• Common Table Expressions (CTEs) (WITH clause) & Recursive CTEs
• Conditional Logic (CASE WHEN ... THEN ... ELSE END)

6. Window Functions (Analytic Functions)

• OVER Clause & Partitioning (PARTITION BY, ORDER BY)
• Ranking Functions (ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE())
• Value Functions (LAG(), LEAD(), FIRST_VALUE(), LAST_VALUE())
• Aggregate Window Functions (SUM() OVER (...), AVG() OVER (...))

7. Database Design & Optimization

• Normalization (1NF, 2NF, 3NF, BCNF) & Denormalization
• Indexing Strategies (B-Tree, Hash, Clustered vs. Non-Clustered Indexes)
• Query Execution Plans & Performance Tuning (EXPLAIN / EXPLAIN ANALYZE)
• Views & Materialized Views

8. Transactions, Security & Programmability

• ACID Properties (Atomicity, Consistency, Isolation, Durability)
• Transaction Control (COMMIT, ROLLBACK, SAVEPOINT)
• Transaction Isolation Levels & Concurrency Control
• Stored Procedures & User-Defined Functions (UDFs)
• Triggers & Database Events

Note: Service Based Companies mostly asked questions on Joins, Keys and Employee table sql quey.

4. Project (1 month)

For project you can ask if your friends working in this domain , you can copy paste the project to add in your resume and understand the project from him and whatever his doing, you can tell same in interview.

Interview just ask “Tell me about your current project”, so you should know the architecture, what are technologies used in project and what you did in project like(Junit, bug fixes, Rest API, Testing)

Important Note : Solve few Coding problem on Arrays and Strings from LeetCode.