Interview Notes

Interview questions and answers

Object-oriented programming(OOPS)

• OOPS
  • Abstraction
  • Encapsulation
  • Polymorphism
  • Abstract Class
  • Does Abstract class have constructor?
  • Abstract class Vs Interface
  • What to choose – interface or abstract class
  • Why Java 8 has introduced default methods?
  • Why Java 8 has introduced static methods?
  • Why Java does not allow multiple inheritance?
  • Method Overloading and Overriding
    • Method Overloading
    • Rules for Method Overloading
    • Method Overriding
    • Rules for Method Overriding
  • Association
  • Aggregation
  • Composition
  • Association vs. Aggregation vs. Composition

Java

• Basic

  • Java 8

    • Java 8 Features

    • New features

    • Lambda Expressions

    • Lambda Expressions

      1. Examples of lambda expressions
      2. Why use Lambda Expression
      3. Lambda Expressions Syntax
      4. Lambda Expressions Examples

    • Stream

      • Stream features

    • Intermediate and Terminal operations

      • Intermediate vs Terminal operations
      • Intermediate Operations
      • Terminal Operations

    • Functional Interface

      • Custom Functional Interface
      • Predefined Functional Interfaces
      • Predicate
      • Function
      • Supplier
      • Consumer
      • BiFunction
      • BiConsumer

    • Method References

      • Method References Types

    • Test

  • Why String is Immutable?
  • StringBuffer and StringBuilder
  • equals and hashcode contract
  • Comparable and Comparator interfaces
    • Comparable vs Comparator
  • static keyword
  • Shallow Copy and Deep Copy
  • Serialization and De-serialization
  • Serialization scenarios with Inheritance
  • How to make a class Immutable?
  • Class loaders in Java
  • Garbage Collector
    • How does the garbage collector work?
    • Types of garbage collectors
    • Garbage Collection and types of Garbage Collectors
    • final, finally and finalize()
  • String, StringBuffer, StringBuilder
  • Reflection
  • Exceptions
    • Checked and Unchecked Exception
    • Custom exception
    • OutOfMemoryError
  • Generics
    • Benefits of Generics
    • Collection Framework examples for Generics.
    • Type Parameter Naming Conventions
    • Multiple Type Parameters
  • Immutable object
    • Benefits of immutable objects
    • Immutable Class
    • Wrong way to write an immutable class
    • Right way to write an immutable class
  • Pass by reference and Pass by value
  • Shallow cloning and Deep cloning
  • Instance variable and a Static variable
  • Local variables vs Instance and static variables
  • Access Modifiers
  • Volatile keyword
  • synchronized vs volatile
  • Test

• Collection Framework

  • ArrayList
    • Accessing elements
    • Removing elements
    • Iterating over an ArrayList
    • Searching for elements in an ArrayList
    • Sorting an ArrayList
  • HashMap
    • HashMap Internal working
    • Sort Map By Value Example
    • How put() method of HashMap works internally
    • How HashMap get() method works internally
    • When null Key is inserted in a HashMap
    • HashMap implementation changes in Java 8
    • Interal working of put() and get() methods of HashMap
    • HashMap collisions
  • equals and hashCode method in HashMap when the key is a custom class
  • Concurrent HashMap
    • ConcurrentHashMap vs Synchronized HashMap
  • HashSet class
  • TreeMap
  • TreeSet
  • fail-safe and fail-fast iterators

• Multi threading

  • Life Cycle of a Thread
  • Creating a Thread
  • Life Cycle of a Thread
  • Creating a Thread
  • Difference between Runnable vs Thread
  • synchronized keyword
  • static synchronization
  • What does join() method?
  • Deadlock
  • How to avoid deadlock?
  • What will happen if I directly call the run() method and not the start() method to execute a thread?
  • Once a thread has been started can it be started again?
  • Why wait, notify and notifyAll methods are defined in the Object class instead of Thread class?
  • Why wait(), notify(), notifyAll() methods must be called from synchronized block?
  • wait() vs sleep() methods
  • Executor Framework
    • High level concurrency features Executor framework
    • Executor Interface
    • ExecutorService Interface
    • ExecutorService Interface Examples
    • Different Between execute() and submit() Methods
    • ScheduledExecutorService Interface
    • Future Interface
    • Executor Framework-2

Data Structures and Algorithms

• Lists

  • ArrayList
  • LinkedList
  • Stack
  • Vector
  • CopyOnWriteArrayList
  • Collections.synchronizedList

• Sets

  • HashSet
    • LinkedHashSet
    • TreeSet
    • ConcurrentSkipListSet
    • CopyOnWriteArraySet
    • EnumSet

• Maps

  • HashMap
  • HashMap implementation details
  • LinkedHashMap
  • Hashtable
  • ConcurrentHashMap
  • TreeMap
  • ConcurrentSkipListMap

• Queues

  • LinkedList
  • ArrayBlockingQueue
  • LinkedBlockingQueue
  • ConcurrentLinkedQueue
  • Deque classes
  • PriorityQueue
  • PriorityBlockingQueue
  • DelayQueue
  • SynchronousQueue

• equals and hashCode

• Hierarchy and classes

• Frequently asked

  • Stack

  • CustomStack

  • LinkedListStack

  • LinkedListReversal

  • MyLinkedList

  • PrimesPrimeChecker

  • RemoveDuplicateFromString

  • Palindrome

  • FindLargestThree

  • FibonacciSeries

  • BalancedBracketsUsingString

  • BalancedBracketsUsingDeque

  • Anagram

    • Problem analysis
    • Code implementation (sorting)
    • Code implementation (hash)

  • Anagrams

    • Anagrams
    • ValidAnagram
    • PrintAnagramTogether
    • AnagramOfFirstAsSubstring
    • GroupAnagramsTogether

  • Find the median of two positively ordered arrays

    • What is the median of an array
    • Problem analysis
    • Code
    • Code (Brute Force approach)

  • Subarray Sum Equals K

    • Problem analysis
    • Code - Optimization by Hashmap
    • Code - Brute Force approach

• Data Types

  • System-defined data types (Primitive data types)
  • User defined data types

• Data Structures

  • Linear data structures

  • Non – linear data structures

  • Commonly Used Rates of Growth

  • Arrays

    • Advantages of Arrays
    • Disadvantages of Arrays
    • Dynamic Arrays

  • Linked List

    • Advantages of Linked List
    • Disadvantages of Linked List
    • Comparison of Linked Lists with Arrays & Dynamic Arrays
    • Test

• Sorting

  • Bubble Sort
    • Implementation
    • Performance
  • Selection Sort
    • Implementation
    • Performance
  • Insertion Sort
    • Advantages
    • Algorithm
    • Implementation
    • Example
    • Analysis
    • Performance
    • Comparisons to Other Sorting Algorithms
  • Shell Sort
    • Implementation
    • Performance
  • Merge Sort
    • Implementation
    • Performance
  • Heap Sort
    • Implementation
    • Performance
  • Quicksort
    • Implementation
    • Performance
  • Tree Sort
    • Implementation
    • Performance
  • Comparison of Sorting Algorithms
  • Test
  • Test
  • Test
  • Test
  • Test

Spring

• Spring
  • Dependency Injection
    • Types of Dependency Injection
    • Constructor-based DI
    • Setter-method injection
    • Constructor Vs Setter injection
  • BeanFactory and ApplicationContext
  • Spring Bean life-cycle
  • Spring Bean Scopes
    • What happens when we inject a prototype scope bean in a singleton scope bean?
    • How to inject a prototype scope bean in a singleton scope bean?
    • Stereotype Annotations
    • @Controller vs @RestController annotation
    • @Qualifier annotation
    • @Transactional annotation
    • @ControllerAdvice annotation
    • @Bean annotation
    • @Component vs @Bean annotation
    • Spring Boot Security using OAuth2 with JWT
    • OAuth2 Terminology
    • Json Web Token(JWT)
    • Spring Boot Rest Authentication with JWT Token Flow
  • Web server vs application server
  • Spring Transaction Management
    • Global Transactions
    • Local Transactions
    • Programmatic Approach:
    • Declarative Approach (@Transactional)
    • propagation
    • isolation
    • readOnly
    • timeout

Spring Annotations

• @Autowired
• @Inject vs @Autowired
• Component Scanning
• @ComponentScan
  • @ComponentScan Without Arguments
  • @ComponentScan With Arguments
  • @ComponentScan with Exclusions
  • @ComponentScan in a Spring-Boot application
• Difference between @Component, @Repository & @Service annotations?
  • @Repository
  • @Service
  • @Controller
  • Test

Spring MVC

• Spring MVC
• Spring MVC flow
• Spring Web Annotations
  • @RequestMapping
  • @RequestBody
  • @PathVariable
  • @RequestParam
  • @ResponseBody
  • @ExceptionHandler
    • @ResponseStatus
  • @Controller
  • @RestController
  • @ModelAttribute
  • @CrossOrigin
  • Scheduler in cluster environment or run on multiple instances
    • Spring Scheduled Task running in clustered environment with ShedLock
    • Configuration
    • Creating Tasks
    • Spring
    • Execute a Quartz Job only once in a multi-instance environment

Spring Boot

• Spring Boot
• Spring Boot Primary Goals
• Running Spring boot app at different port on server startup
• Key Spring Boot features
• Spring Boot Starters
• Spring Boot Autoconfiguration
• Easy-to-Use Embedded Servlet Container Support
• Spring Boot Annotations
  • @SpringBootApplication
    • @EnableAutoConfiguration
    • @ConditionalOnClass and @ConditionalOnMissingClass
    • @ConditionalOnBean and @ConditionalOnMissingBean
    • @ConditionalOnProperty
    • @ConditionalOnResource
    • @ConditionalOnWebApplication and @ConditionalOnNotWebApplication
    • @ConditionalExpression
    • @Conditional
  • Spring Boot Actuator
    • pring-boot-actuator maven dependency
    • Predefined Endpoints
    • /info Endpoint
    • /metrics Endpoint
    • Custom Endpoint
• Building an Application with Spring Boot
  • Starting with Spring Initializer
  • Create a Simple Web Application
  • Create an Application class
  • Run the Application
  • Add Unit Tests
  • Add Production-grade Services
• Spring Boot CRUD Web Application with Thymeleaf, Spring MVC, Spring Data JPA, Hibernate, MySQL
  • Create Spring Boot Project
  • Maven Dependencies
  • Configure and Setup MySQL Database
  • Model Layer - Create JPA Entity
  • Repository Layer
  • Service Layer
  • Controller Layer
  • View Layer: Thymeleaf
  • Run Spring application and demo
  • Unit Testing REST APIs
  • CrudRepository vs. JpaRepository

Spring AOP(Aspect Oriented Programming)

• Spring AOP(Aspect Oriented Programming)

HTTP methods overview

• HTTP methods overview
  • Idempotency in HTTP
  • Safe Methods
  • Why DELETE method is defined as idempotent
  • Why PATCH method is not idempotent
  • Why is PUT idempotent?

HTTP Status Codes

• HTTP Status Codes

  • 1×× Informational

  • 2×× Success

    • 200 OK
    • 201 Created
    • 202 Accepted
    • 204 No Content
    • 205 Reset Content

  • 3×× Redirection

    • 300 Multiple Choices

  • 4×× Client Error

  • 5×× Server Errorl

Hibernate

• Hibernate
  • JPA vs Hibernate
  • @Entity annotation
  • @Id & @GeneratedValue
  • get() and load() methods of Hibernate Session
  • Session and SessionFactory
  • First Level and Second Level Cache
  • Test

Angular

• Single-page application(SPA) vs. Multiple-page application(MPA)
  • Single-page application(SPA)
  • Pros of the Single-Page Application
  • Cons of the Single-Page Application
  • Multiple-page application(MPA)
  • Pros of the Multiple-Page Application
  • Cons of the multiple-page application
• Angular
  • AngularJS vs Angular
    • AngularJS
    • Angular
    • Why Angular
      • Components
      • Templates
      • Dependency injection
      • Angular Routing and Navigation
    • Angular Module
    • Bootstrapping Module
    • JIT vs AOT compilation
    • Advantages of AOT
    • What are the ways to control AOT compilation?
    • How to optimize loading large data in angular?
    • How an Angular application gets started or loaded?
    • Angular Services
    • What is Interpolation
    • Angular Routing and Navigation
    • Angular Component
      • What Is an Angular Component?
        • Template
        • Class
        • Component Metadata
      • Communication Between Components
        • Parent to Child
        • Child to Parent
        • Child to Parent
        • Unrelated Components
    • Angular Directive
      • Components Directives
      • Structural Directives
      • Attribute Directives
      • How to Create Custom Directives?
      • Structural Directive vs Attribute Directive
      • Component vs Directive
    • Angular Pipes
      • Syntax to use Pipes in Angular Application
      • Types of Pipes in Angular
        • 1. Built-in Pipes
        • 2.Custom Pipes
      • Parameterized Pipe
      • Custom Pipe
      • Pure vs Impure Pipe
    • Angular Data Binding
      • 1. Interpolation
      • 2. Property binding
      • 3. Event binding
      • 4. Two-way data binding
    • Angular Lazy Loading
    • Angular Lifecycle Hooks
      • ngOnChanges
      • ngOnInit
      • ngDoCheck
      • ngAfterContentInit
      • ngAfterContentChecked
      • ngAfterViewInit
      • ngAfterViewChecked
      • ngOnDestroy
      • constructor() vs ngOnInit()
    • RxJS
      • Utility functions provided by RxJS
      • RxJS Operator
      • What is subscribing
      • Observable
      • Observer
      • Error handling in observables
      • Observable creation functions
      • What will happen if you do not supply handler for observer?
      • Promise vs Observable
      • Async Pipe
      • HttpClient
        • Error handling

Design Patterns

• Design Patterns
  • Creational Design Patterns
    • Simple Factory
    • Factory Method
    • Abstract Factory
    • Builder
    • Prototype
    • Singleton
    • singleton class vs a static class
    • Structural Design Patterns
      • Adapter
      • Bridge
      • Composite
      • Decorator
      • Facade
      • Flyweight
      • Proxy
    • Behavioral Design Patterns
      • Chain of Responsibility
      • Command
      • Iterator
      • Mediator
      • Memento
      • Observer
      • Visitor
      • Strategy
      • State
      • Template Method

• Designing a Java/J2EE application

  • Create a tiered architecture
  • Create a data model
  • Create a design model
  • Design considerations when decomposing business use cases into relevant classes
  • Vertical slicing
  • Ensure the system is configurable
  • Design considerations during design, development and deployment phases

• Identifying performance and/or memory issues in your Java/J2EE application

Microservices

• Microservices

  • SOA(Service-oriented architecture) vs Microservices

  • Advantages of Microservices Architecture

  • Disadvantages of Microservices

  • Challenges of Microservices Architecture

  • Gateway

  • Microservices Monitor

  • Microservices vs Monolithic Architecture

  • How does Microservice Architecture work?

  • Communicating Between Microservices

  • SOAP vs REST

  • Eureka Naming Server

  • Zuul

  • Zipkin

  • Versioning of microservices

  • How to send custom business errors or exceptions from a RESTful microservice to client application?

  • What are best practices for microservices architecture?

  • Microservices caching

  • SOLID (solid design principles)

  • How frequent a microservice be released into production?

  • How to achieve zero-downtime during the deployments?

    • Blue-green deployment

  • How to slowly move users from older version of application to newer version?

  • How will you monitor fleet of microservices in production?

  • How will you troubleshoot a failed API request that is spread across multiple services?

  • What are different layers of a single microservice?

  • Spring Cloud

  • application.yml vs bootstrap.yml

  • Netflix Eureka Server : implement service discovery in microservices architecture

    • Netflix Eureka Server
    • Consul Server
    • How does Eureka Server work?

  • Externalize configuration in a distributed system

  • @RefreshScope : Refresh configuration changes on the fly in Spring Cloud environment

  • Achieve client side load balancing in Spring Microservices using Spring Cloud

  • client side load-balancer Ribbon in your microservices architecture

  • Use both LoadBalanced as well as normal RestTemplate object in the single microservice

  • Use of Eureka for service discovery in Ribbon Load Balancer

  • Managing transactions

    • ACID Transactions
    • What is a distributed transaction?
    • Two-phase commit (2pc) pattern
    • Benefits of using 2pc
    • Disadvantages of using 2pc
    • Saga pattern
    • Advantages of the Saga pattern
    • Disadvantages of the Saga pattern
    • Test
    • Test

  • Security in Microservices

    • Why Basic Authentication is not suitable in Microservices Context?
    • Why OAuth2?
    • OAuth2 Roles
    • OAuth 2.0 grant types (OAuth flows)
    • When shall I use resource owner credentials?
    • When shall I use Authorization Code grant?
    • When shall I use client credentials?
    • OAuth2 and Microservices
    • What is JWT?
    • What are use cases for JWT?
    • How does JWT looks like?
    • What is AccessToken and RefreshToken?
    • How to use a RefreshToken to request a new AccessToken?
    • How to call the protected resource using AccessToken?
    • Can a refreshToken be never expiring? How to make refreshToken life long valid?
    • Generate AccessToken for Client Credentials.
    • Why there is no RefreshToken support in Oauth2 Client Credentials workflow?
    • Security in inter-service communication

API Gateway

• API Gateway
• How to retry failed requests at some other available instance using Client Side Load Balancer?
• Circuit Breaker
• What is difference between using a Circuit Breaker and a naive approach where we try/catch a remote method call and protect for failures?
• Circuit Breaker Pattern
• Open, Closed and Half-Open states of Circuit Breaker
• Use-cases for Circuit Breaker Pattern
• Benefits of using Circuit Breaker Pattern
• What is Hystrix?
• Features of Hystrix library
• How to use Hystrix for fallback execution?
• When not to use Hystrix fallback on a particular microservice?
• ignore certain exceptions in Hystrix fallback execution
• Request Collapsing feature in Hystrix
• Circuit Breaker vs Hystrix
• Where exactly should I use Circuit Breaker Pattern?
• Where it should not be used?

Kafka

• Kafka
  • Advantages of Kafka
  • Offset in Kafka
  • Consumer group in Kafka
  • ZooKeeper in Kafka
  • Can I use Kafka without Zookeeper?
  • What is Zookeeper in Kafka? Can we use Kafka without Zookeeper?
  • Partition in Kafka
  • APIs of Kafka
    • Load balancing of the server in Kafka
    • Retention period in Kafka cluster
    • RabbitMQ vs Apache Kafka
    • Explain Apache Kafka Use Cases?
    • Kafka Cluster, and its key benefits
    • Replicas in Kafka
    • Starting a Kafka server
    • In the Producer, when does QueueFullException occur?
    • Confluent Kafka vs. Apache Kafka

MongoDB

• MongoDB
  • Key Components
  • Document
  • Collection
  • Namespace
  • Databases in MongoDB
  • Mongo Shell
  • Advantages of MongoDB:
  • Features of MongoDB
  • Indexes in MongoDB
  • MongoDB

Database

• Database

• SQL

  • Joins

    • Inner join
    • Left outer join
    • Right outer join
    • Full join
    • Cross join
    • Self Join

  • Keys

  • Indexes

    • Non-clustered index
    • Clustered index
    • Composite index
    • Cardinality
    • Bitmap-index
    • Data structures used
    • SQL - Indexes
    • The CREATE INDEX Command
    • Unique Indexes
    • Composite Indexes
    • Implicit Indexes
    • The DROP INDEX Command
    • When should indexes be avoided?

  • Queries

  • SQL vs NoSQL

    • SQL
    • NoSQL
    • SQL vs NoSQL
    • Database Types
    • Schema
    • Data Model
    • Ability to Scale
    • ACID vs BASE
    • Use Cases
    • Reasons to use an SQL database
    • Reasons to use a NoSQL database

• UNION vs UNION ALL

• TRUNCATE vs DELETE, vs DROP

• TRUNCATE

• DELETE

• DROP

  • Frequently asked queries
    • Find all departments with sales more than 1000
    • Print all employee ids with their manager ids
    • Print all manager names with count of directs
    • Find Nth highest salary in SQL - Oracle, MSSQL and MySQL -Nth maximum salary in MySQL using LIMIT keyword -2nd highest salary in MySQL without subquery -3rd highest salary in MySQL using LIMIT clause -Test -Test -Test -Test

Maven

• Maven
• pom.xml
• Maven build life-cycle
  • validate
  • compile
  • test
  • package
  • verify
  • install
  • deploy

Unix

• Unix
  • Find
  • Search
  • Processes
  • File permissions
  • List files
  • Symlinks
  • Checking logs
  • Text manipulation
  • Sed
  • Networking
  • Space
  • Miscellaneous

DevOps Tools

• Docker
• Git
  • Advantages of git
  • git push
  • git pull vs git fetch
  • conflict
  • resolve a conflict
  • git clone
  • git pull origin
  • git commit a
• Jenkins
  • Continuous delivery
• Kubernetes

Swagger

• Swagger
• Integrate Swagger into your microservices
• Swagger annotations
  • @Api
  • @ApiOperation
  • @ApiResponse
  • @ApiParam
• Maven plugin

Cucumber

• Cucumber
• Advantages of Cucumber
• Example
• Features in Cucumber
• Feature file
• Step Definition
• Gherkin
• user login feature Example
• Test harness in Cucumber
  • Selenium vs Cucumber
  • TDD(Test-Driven Development)
  • BDD and TDD
  • Cucumber profiles
  • Scenario Outline
  • Scenario and Scenario Outline
  • Step Definition
  • Background in a Feature file
  • Junit Test runner class
  • Tags in cucumber-bdd
  • Cucumber Hooks
  • Name any two testing framework that can be integrated with Cucumber?
  • What are the two files required to run a cucumber test?
  • Examples Table or Scenario Outline vs Data Table

Agile

• Agile Scrum Ceremonies
  • Sprint Planning
  • Daily Scrum
  • Sprint Review
  • Sprint Retrospective

Amazon Web Services (AWS)

• AWS

• Key components of AWS

• Elastic Cloud Compute (EC2)

• Simple Storage Service (S3)

  • Objects and Buckets
  • S3 Storage Classes
  • Durability and Availability
  • Storage Classes for Frequently Accessed Objects
  • Storage Classes for Infrequently Accessed Objects
  • Storage Class for Both Frequently and Infrequently Accessed Objects
  • Access Permissions
    • Bucket Policies
    • User Policies
    • Bucket and Object Access Control Lists
    • Encryption
    • Versioning

• Relational Database Service (RDS)

  • Database Engines
  • Licensing
  • Instance Classes
  • Standard
  • Memory Optimized
  • Burstable Performance
  • Scaling Vertically
  • Storage
  • General-Purpose SSD
  • Provisioned IOPS SSD
  • Magnetic
  • Scaling Horizontally with Read Replicas
  • High Availability with Multi-AZ
  • Backup and Recovery

• Route 53

• CloudWatch

  • CloudWatch Metrics
  • CloudWatch Alarms
  • CloudWatch Dashboards
  • CloudWatch Logs
  • Metric Filters
  • CloudWatch Events

• CloudTrail

  • API and Non-API Events
  • Management and Data Events
  • Event History
  • Trails
  • Log File Integrity Validation

• Cost Explorer

  • Cost and Usage
  • Reservation reports
  • Reserved Instances Utilization
  • Reserved Instances Coverage
  • Reserved instance recommendations

• Amazon DynamoDB

  • Items and Tables
  • Scaling Horizontally
  • Queries and Scans

• AWS Lambda

  • Introducing AWS Lambda
  • Key benefits of serverless computing
    • No ware to manage:
    • Faster execution time:
    • Really low costs:
    • Support of popular programming languages:
    • Microservices compatible:
    • Event-driven applications:
  • Cons or Disadvantage of serverless computing
    • Execution duration:
    • Complexity:
    • Lack of tools
    • Vendor lock-in:
  • Test
  • Test
  • Test

Good Practices

• Good Practices for REST API Design
  • Accept and respond with JSON
  • Use nouns instead of verbs in endpoint paths
  • Nesting resources for hierarchical objects
  • Handle errors gracefully and return standard error codes
  • Allow filtering, sorting, and pagination
  • Maintain Good Security Practices
  • Cache data to improve performance
  • Versioning our APIs
• Java code review checklist
  • Basic Checks (before)
  • The code was tested
  • Clean Code
  • Best Practices
  • Exception Handling
• Common Java Vulnerabilities
  • Injection Flaws
  • Cross Site Scripting (XSS)
    • How does XSS work?
  • Cross Site Request Forgery(CSRF)
  • Test
• Resolving a Production Issue on a Live Server
  • Notify All Stakeholders
  • Reproduce : Replicate the production environment locally
  • Root Cause Analysis & Fix
  • Re-test & Regression Testing
  • Backup the System Before Implementing Complex Solution
  • Document the Problem and How it was Resolved