Java & Spring Boot Interview Preparation Bootcamp

Code Katha

Java & Spring Boot Interview Preparation Bootcamp

Bootcamp Overview

Step-by-Step Learning: Comprehensive training in Java and Spring Boot to prepare for job interviews with confidence.

Proven Success Tips: Learn from my experience of clearing interviews at top companies like Publicis Sapient, MakeMyTrip, EPAM Systems, Samsung, UST Global, Cognizant, Deloitte, and Expedia, where i got almost 200% hike with fixed component.

Master Core Topics: Gain expertise in Core Java, Multithreading, Collections, Kafka, Databases (MongoDB, MySQL), Caching, Cloud, AI, and Spring Boot through simple explanations and practical examples.

Problem-Solving Skills: Enhance your coding skills with Java 8+ features like streams and operators that are highly valued in interviews today.

Hands-On Coding Sessions: Build confidence and clarity with live coding examples and step-by-step practice.

Hindi Video Lectures: Understand complex topics easily with video lectures and notes.

Java

SOLID Principles and OOPS

SOLID Principles

SOLID principles are the foundation of object-oriented design, aimed at improving code maintainability and scalability.

These principles include Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion.

By following these principles, developers can write flexible and robust code that adapts to changing requirements.

Interfaces

Interfaces in Java define contracts that classes can implement, allowing for abstraction and multiple inheritance. They enable loose coupling between components, making systems more modular and testable.

Serializable

The Serializable interface in Java allows objects to be converted into a byte stream, making it possible to save them to a file or send them over a network. This process is crucial for persistent data storage and communication between distributed systems.

Serialization is commonly used in frameworks like Hibernate, where objects are saved to databases. It also supports deep cloning of objects. However, it is important to handle serialization carefully to ensure security and data integrity.

Cloning

Cloning in Java is a process of creating an exact copy of an object. This is achieved using the Cloneable interface and the clone() method.

Shallow cloning copies the object's fields but not the objects they reference, whereas deep cloning creates independent copies of all referenced objects. Cloning is often used in scenarios where duplicate objects need to be manipulated independently, such as prototyping patterns.

Understanding cloning helps in creating efficient solutions while avoiding common pitfalls like unexpected modifications.

Generics

Generics enable type safety in Java by allowing classes and methods to operate on specific data types while maintaining code reusability. For example, a List<String> ensures only strings can be added to the list, reducing runtime errors.

Generics are widely used in collections and custom classes for creating flexible and type-safe APIs. Understanding how generics work, including wildcards and bounded types, is essential for writing robust and scalable applications.

Internal Libraries

Java provides a rich set of internal libraries that simplify common tasks such as string manipulation, date and time handling, and concurrency management.

Libraries like java.util, java.time, and java.util.concurrent offer prebuilt classes and methods to enhance productivity. For instance, the java.util.ArrayList class allows dynamic array manipulation, and the java.time.LocalDate class simplifies date management.

Familiarity with these libraries is a must for efficient Java programming.

Access Modifiers

Access modifiers in Java control the visibility and accessibility of classes, methods, and variables.

The four main modifiers are public, protected, private, and default (package-private). These modifiers help encapsulate data and define how different parts of a program interact with each other.

For example, private restricts access to the declaring class, while public allows access from anywhere. Understanding access modifiers ensures secure and modular code design.

Enums

Enums in Java represent a fixed set of constants, making your code more readable and type-safe. For instance, an enum for days of the week (MONDAY, TUESDAY, etc.) can be used to avoid invalid values like "Funday."

Enums can also have methods, fields, and constructors, allowing you to associate specific behavior or data with each constant.

They are widely used in scenarios like status codes, state machines, and configuration settings.

Collections

HashMap Internals, Collision, and Load Factor

HashMap is one of the most widely used data structures in Java. It uses hashing to store and retrieve key-value pairs efficiently. Understanding HashMap internals involves learning about hash functions, collision resolution using chaining or open addressing, and resizing mechanisms to maintain performance. Knowing how HashMap works under the hood helps in optimizing its usage in real-world applications.

Hash collisions occur when two keys generate the same hash code, causing them to map to the same bucket in a HashMap. Java handles collisions using linked lists (or trees in modern implementations). Knowing how to minimize collisions by choosing effective hash functions and understanding collision resolution techniques ensures optimal performance of hash-based collections.

Load factor determines when a HashMap should resize its capacity to maintain performance. A lower load factor leads to fewer collisions but consumes more memory, while a higher load factor reduces memory usage but increases collision probability. By default, Java HashMap uses a load factor of 0.75. Understanding load factor helps in fine-tuning HashMap performance for specific use cases.

ArrayList vs LinkedList

ArrayList and LinkedList are two commonly used list implementations in Java. ArrayList uses a dynamic array internally, making it efficient for random access and iteration. LinkedList, on the other hand, uses a doubly-linked list structure, making it better suited for frequent insertions and deletions. Understanding their differences helps in choosing the right implementation based on application requirements.

Concurrent Modification Exception

ConcurrentModificationException occurs when a collection is modified while iterating over it using an iterator. This exception helps maintain consistency and prevents unexpected behavior. To handle it, you can use concurrent collections like CopyOnWriteArrayList or synchronized blocks. Understanding this exception is crucial for developing robust multithreaded applications.

LinkedHashMap Internals

LinkedHashMap extends HashMap to maintain insertion or access order of entries. This is achieved using a doubly-linked list that connects entries in the desired order. It is commonly used when predictable iteration order is required, such as implementing caches. Understanding LinkedHashMap internals is essential for scenarios requiring both performance and ordering.

Java 8

Streams API

Java 8 Streams API is a powerful feature for processing data in a declarative way. It allows developers to perform operations like filtering, mapping, and reducing on collections and arrays. Streams enable parallel execution, improving performance in large datasets. Understanding intermediate operations like filter() and map() and terminal operations like collect() and forEach() is essential for writing efficient and readable code.

Predicates

Predicates in Java 8 are functional interfaces that represent a condition or a test. They are commonly used in Streams API to filter data based on certain conditions. For example, a predicate isEven can be used to filter even numbers from a list. Understanding predicates helps in creating concise and expressive code while leveraging functional programming techniques.

Functional Interfaces

Functional interfaces in Java 8 are interfaces with a single abstract method, enabling the use of lambda expressions. Examples include Runnable, Callable, and custom interfaces like Comparator. They play a crucial role in functional programming, making code more readable and concise. Learning functional interfaces helps in leveraging Java 8's modern programming features effectively.

Intermediate and Terminal Operations

Intermediate operations in Streams API, such as map(), filter(), and sorted(), transform data without terminating the stream. Terminal operations, like collect(), forEach(), and reduce(), process and produce a final result. Understanding the difference between these operations is crucial for writing efficient and reusable data processing pipelines.

Design Patterns

Singleton

The Singleton design pattern ensures that a class has only one instance and provides a global point of access to it. It is widely used for scenarios like managing configurations, logging, or database connections. Implementing Singleton correctly requires handling multithreading and serialization issues. Understanding this pattern is essential for building efficient and controlled object management.

Other Design Patterns

Design patterns like Factory, Builder, and Observer provide proven solutions to common problems in software design. For example, the Factory pattern creates objects without specifying their exact class, while the Observer pattern establishes a subscription mechanism. Learning these patterns helps in writing flexible and maintainable code for real-world applications.

Multithreading

Future and CompletableFuture

Future and CompletableFuture are used for asynchronous programming in Java. While Future represents the result of an asynchronous computation, CompletableFuture allows chaining multiple asynchronous tasks. It is commonly used in scenarios like web service calls or file processing, where tasks can run in parallel to improve efficiency. Understanding these concepts is essential for building responsive and scalable applications.

Callable

The Callable interface in Java represents tasks that return a result and can throw exceptions. Unlike Runnable, it provides greater flexibility and is widely used with ExecutorService to manage thread pools. Callable is crucial for implementing multithreaded applications that require task results or error handling.

Executor Service

ExecutorService is a framework for managing and controlling thread pools in Java. It provides methods for submitting tasks, shutting down threads, and monitoring progress. Understanding how to use ExecutorService helps in optimizing resource usage and avoiding common pitfalls like thread leakage.

Parallel Streams

Parallel streams in Java enable concurrent data processing by leveraging multiple threads. They are ideal for large datasets, as they split the data into chunks and process them in parallel. Understanding parallel streams involves learning about thread safety and managing shared resources to ensure correct and efficient execution.

Messaging Questions

Message Queues Overview

Message Queues (MQs) like RabbitMQ, Kafka, ActiveMQ, and Amazon SQS are essential for asynchronous communication between distributed systems. They decouple producers and consumers, enhancing scalability and fault tolerance. Understanding the differences between point-to-point and publish/subscribe models is crucial for selecting the appropriate MQ for your architecture.

Integrating MQ with Spring Boot

Learn how to integrate popular MQ systems with Spring Boot applications using configurations and libraries like Spring AMQP and Spring Kafka. This involves setting up producers, consumers, and retry mechanisms to ensure reliable message processing.

Database

Query Writing

Master writing efficient SQL queries to retrieve, manipulate, and analyze data. Topics include joins, subqueries, and using aggregate functions for reporting. SQL proficiency is a must-have skill for backend developers.

Table Relationships

Understand how to define and manage relationships between tables, such as one-to-one, one-to-many, and many-to-many. Using tools like foreign keys ensures data integrity and supports complex queries.

Indexing

Indexes improve query performance by optimizing data retrieval. Learn about different types of indexes like B-trees and hash indexes, and when to use them for optimal database performance.

Transactions and Hibernate

Explore local transactions and how Hibernate ORM manages persistence. Topics include session management, transaction propagation, and handling lazy loading in complex queries.

Profiler, JVM, and GC

Understanding Profilers

Profilers like VisualVM and JProfiler help identify bottlenecks in applications by monitoring CPU, memory, and thread usage. Learning to interpret profiling data is key to optimizing application performance.

Thread Dumps

Thread dumps provide insights into the state of threads in a running JVM. Learn how to capture and analyze thread dumps to debug deadlocks and performance issues.

Garbage Collection (GC)

Gain a deep understanding of how JVM garbage collection works, including GC algorithms like G1, CMS, and Parallel GC. Learn to configure JVM options for better performance.

JVM Configurations

JVM tuning involves configuring heap size, garbage collection, and other parameters. Learn how to use JVM options to optimize application runtime behavior.

Solution

Understanding Application Layers

Learn how to break down an application into layers such as presentation, business logic, and data access. Understanding these layers helps in maintaining clean and scalable code architecture.

Non-Functional Requirements

Explore key non-functional requirements like monitoring, security, and scalability. Learn how to use tools like Grafana and Prometheus for monitoring system performance.

Production Support

Understand the essentials of production support, including log analysis, release management, and handling rollback scenarios. These skills ensure seamless application deployment and maintenance.

Microservices

REST Principles

Master the principles of RESTful API design, including statelessness, resource identification, and standard HTTP methods. Learn how to use tools like Swagger for API documentation.

Microservices Patterns

Explore common microservices patterns such as service discovery, circuit breakers, and API gateways. Tools like Netflix Eureka, Hystrix, and Spring Cloud Gateway simplify microservices communication.

Caching

Learn about caching techniques using tools like Redis and Ehcache. Understand how caching improves performance by reducing database load and speeding up data retrieval.

API Security

API security involves implementing authentication and authorization mechanisms like JWT, OAuth2, and Basic Auth. Learn how to secure APIs using Spring Security and integrate with identity providers.

Cloud Deployment

Understand the basics of deploying applications on cloud platforms like AWS, GCP, and Azure. Topics include containerization with Docker and using Kubernetes for orchestration.

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