Java Interview Questions

Top Java Interview Questions up to 5 Years Experience (2026 Guide)

Top Java interview questions upto 5 years experience including Java developer interview questions, Core Java interview questions, Spring Boot interview questions, and Java coding interview questions. Prepare for your next interview with real-world examples and expert answers.

Java Interview Topics up to 5 Years Experience

Looking for Java interview questions up to 5 years experience ? This guide covers Core Java, Spring Boot, Microservices, and real-world Java developer interview questions asked in top companies.

Category	Topics
Core Java	Basics | OOPs | Stream API | Collections
Spring Boot	Annotations | REST APIs | Spring Data JPA
Microservices	Architecture | API Gateway
DevOps	Docker | Kubernetes
System Design	Load Balancing | Caching Strategies | Database Sharding & Partitioning | Horizontal vs. Vertical Scaling | Microservices vs. Monolith | Design a Rate Limiter | CAP Theorem: | DNS & Load Balancing
Database	SQL | Joins

☕ Java Basics (Top 5 Preview)

Why is Java platform independent?

Java uses Bytecode which runs on any system with a JVM...

How does the Garbage Collector (GC) decide which Java objects to clean?

In Java, the Garbage Collector identifies "dead" objects that are ....

Difference between JDK and JRE?

JDK is for development, JRE is for running apps...

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🏗️ OOPS Concepts (Top 5 Preview)

What is Polymorphism?

It is the ability of an object to take many forms...

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🍃 Spring Boot (Top 5 Preview)

What is the difference between Spring and Spring Boot? Easy

Spring is a Java framework that requires heavy XML or Java-based configuration. Spring Boot is built on top of Spring and uses "Opinionated Defaults" to provide Auto-configuration and Embedded Servers (Tomcat), allowing you to build production-ready apps instantly.

How does Dependency Injection (DI) work in Spring? Medium

Dependency Injection is a design pattern where the Spring IoC (Inversion of Control) Container creates and manages objects (Beans) and "injects" them into your class.


It can be done via Constructor, Setter, or Field injection (using @Autowired).

What is the use of @RestController and @RequestMapping? Medium

• @RestController: Combines @Controller and @ResponseBody. It ensures the return data is automatically converted to JSON/XML.
• @RequestMapping: Used to map web requests to specific handler methods. (Modern versions use @GetMapping, @PostMapping, etc.)

Explain the Bean Lifecycle in Spring. Hard

The Spring Bean life cycle consists of:

1. Instantiation: Bean object is created.
2. Populate Properties: Dependency Injection happens.
3. Initialization: @PostConstruct or InitializingBean methods run.
4. In Use: Bean is ready for the app.
5. Destruction: @PreDestroy runs before the bean is removed from the container.

[Image of Spring Bean Lifecycle diagram]

What is Spring Boot Actuator? Hard

Spring Boot Actuator provides "production-ready" features to help you monitor and manage your application. It exposes HTTP Endpoints like:

• /health: Shows if the app and DB are up.
• /metrics: Shows CPU, Memory, and HTTP traffic stats.
• /env: Shows current environment properties.

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🏗️ System Design Basics (Top 5 Preview)

What is the difference between Vertical and Horizontal Scaling? Easy

Vertical Scaling (Scaling Up) means adding more power (CPU, RAM) to an existing server. Horizontal Scaling (Scaling Out) means adding more servers to your network to share the load.

• Vertical: Has a hard limit (you can only buy a server so big) and causes downtime.
• Horizontal: Is theoretically infinite and provides better High Availability.

What is a Load Balancer and why is it used? Medium

A Load Balancer acts as a "traffic cop" sitting in front of your servers. It routes incoming client requests to all servers capable of fulfilling those requests.


Key Benefits:

• Prevents any single server from becoming a bottleneck.
• Improves application availability (if one server fails, the LB sends traffic to others).
• Allows for "Zero Downtime" deployments.

Explain the CAP Theorem in simple terms. Hard

The CAP Theorem states that a distributed system can only provide two out of the following three guarantees at the same time:

• Consistency (C): Every read receives the most recent write or an error.
• Availability (A): Every request receives a (non-error) response, without the guarantee that it contains the most recent write.
• Partition Tolerance (P): The system continues to operate despite an arbitrary number of messages being dropped by the network between nodes.

In the real world, network partitions are inevitable, so we usually choose between CP or AP.

What is Caching and where can we apply it? Medium

Caching is the process of storing copies of data in a temporary storage layer (like RAM) so that future requests for that data can be served faster.

Where to apply:

• Client Side: Browser cache.
• CDN: Serving images/videos from a location closer to the user.
• Application Level: Using Redis or Caffeine to store database query results.
• Database Level: Internal buffer pools.

What is Database Sharding? Hard

Sharding is a type of horizontal scaling for databases. It involves breaking up a large database into smaller, faster, and more easily managed parts called shards.


How it works: Data is typically split based on a "Shard Key" (e.g., User ID 1-1000 goes to Shard A, 1001-2000 goes to Shard B). This prevents any single database server from running out of disk space or processing power.

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Frequently Asked Questions (FAQ)

What are Java interview questions for 5 years experience?

These include Core Java, Spring Boot, multithreading, collections, and real-world coding interview questions.

Is Spring Boot important for Java interviews?

Yes, Spring Boot is widely used in industry and most companies expect strong knowledge of it.

What topics should I prepare for Java interviews?

You should prepare Core Java, OOPs, collections, multithreading, Spring Boot, REST APIs, and database concepts.

How to crack Java developer interviews?

Practice coding, understand concepts deeply, revise frequently asked questions, and work on real projects.

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