Java interviews in 2026 look different from a few years ago. Core Java still matters, but interviewers increasingly test Spring Boot, concurrency reasoning, and how you explain a real project. Here is what actually comes up, based on what clients ask our candidates.
Core Java (still the filter)
- How does a HashMap work internally? What changed in Java 8?
- equals() and hashCode() – the contract, and what breaks if you violate it.
- String immutability, StringBuilder vs StringBuffer.
- Checked vs unchecked exceptions; try-with-resources.
- Generics, type erasure, and when you would use wildcards.
- Java 8+ features: streams, Optional, lambdas, functional interfaces. Expect a live-coding variant.
Concurrency
- synchronized vs ReentrantLock – when and why.
- ExecutorService and thread pools; why not create raw threads.
- CompletableFuture for async pipelines.
- Race conditions and deadlocks – be ready to spot one in a code snippet.
JVM and performance
- Heap vs stack; how garbage collection works at a high level.
- Common causes of memory leaks in Java applications.
- How you would investigate a slow endpoint or high CPU in production.
Spring Boot and microservices
- Dependency injection and bean scopes.
- Building a REST API: controllers, validation, exception handling.
- Spring Data JPA basics; the N+1 problem.
- Service-to-service communication, circuit breakers, and config management.
Coding rounds
Arrays, strings, and hash maps dominate. Practice problems where you explain time and space complexity out loud – interviewers score the explanation as much as the code.
The project deep-dive
Almost every serious interview includes a walk-through of something on your resume. Know your architecture, why specific choices were made, what broke, and what you would do differently. This is where offers are won or lost.
How to prepare
Two weeks of focused prep beats two months of passive reading. Alternate days: one day core concepts, one day coding practice, and rehearse your project story until it is tight.
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