Java developer
As a Java developer,
Please learn:
Core Java (OOP, Collections, Multithreading, JVM internals)
Spring Boot (REST APIs, Dependency Injection, Security)
APIs (REST, GraphQL, gRPC in Java ecosystem)
Database Systems (JDBC, JPA/Hibernate, SQL vs NoSQL)
Distributed Systems (scalability, microservices with Spring)
Caching (Redis with Spring Cache)
Security (Spring Security, JWT, OAuth2)
DevOps (Dockerizing Java apps, CI/CD, Kubernetes basics)
Performance Optimization (JVM tuning, profiling, GC tuning)
Messaging (Kafka, RabbitMQ with Java)
Cloud (AWS/GCP with Java services)
Monitoring (Actuator, Prometheus, Grafana)
Pick one language.
Go deep.
Stop jumping from one language to another.