Java developer interviews usually test a combination of Core Java, object-oriented programming, collections, exception handling, multithreading, SQL, Spring Boot, REST APIs, and basic problem-solving skills.
Freshers should first build a strong understanding of Java fundamentals such as inheritance, polymorphism, abstraction, interfaces, String, collections, and exception handling. After that, move toward Spring Boot, REST APIs, JPA, Hibernate, and database concepts.
Do not prepare only theoretical questions. Build at least one small application containing authentication, CRUD APIs, database integration, validation, and proper exception handling. Being able to explain your own project clearly can make a significant difference during interviews.