This page has been translated to Chinese by monklof.

I'm not a big fan of asking technical questions in job interviews: I'd rather prefer to sit together with candidates in front of some real code, facing a real problem, and have a full day of pair programming rotating with all the team members. Yet, some technical questions could be used to start a deep and nice conversation, and this can be useful to get a deeper knowledge of each other.

• 나는 구직 인터뷰를 위한 기술 질문 덕후는 아니다. 차라리 면접자와 같이 리얼 코드 앞에 앉아서, 실제 문제를 마주하고, 그리고 모든 팀 멤버와 하루종일 페어 프로그래밍을 하는 것을 선호하다. 여전히, 몇몇 기술적 질문으로 깊고 좋은 인터뷰를 시작하는데 익숙하고, 서로 깊은 지식을 얻는데 유용하다.

This repo contains a number of backend interview questions that can be used when vetting potential candidates. It is by no means recommended to use every single question here on the same candidate (that would take hours). Choosing a few items from this list should help you vet the intended skills you require.

• 이 저장소는 인터뷰시에 사용 될 만한 몇가지 백엔드 인터뷰 질문을 담고 있다. 동일한 인터뷰 후보자에게 모든 질문을 사용하는 것은 바람직하지 않습니다(많은 시간이 걸린다). 이 목록에서 몇 가지 항목을 선택하여 인터뷰 후보자에게 기대하는 기술을 확인하는 데 도움이 됩니다.

This project is admittedly inspired by Front-end Job Interview Questions by @darcyclarke

• 이 프로젝트는 다음 저장소의 영감을 받아 작성되었습니다.

Note: Keep in mind that many of these questions are open ended and could lead to interesting discussions that tell you more about the person's capabilities than a straight answer would. Again, I stress that just asking question is hardly sufficient. Complete the interview with a long pair programming session with your candidates: it is one of the best opportunities to know each other's style and approach and to let candidates know some details about their future day job.

• 주의 이 질문 중 많은 부분은 정해진 답이 없으므로 직접적인 대답보다 능력에 대해 더 많이 알려주는 흥미로운 토론으로 이어질 수 있음을 명심하십시오. 다시 한 번 강조하지만, 질문하는 것만으로는 충분하지 않습니다. 후보자와 긴 페어 프로그래밍 세션 인터뷰를 완료하십시오 : 이는 서로의 스타일과 접근 방식을 알고 후보자가 미래의 직업에 대한 세부 정보를 알 수있는 가장 좋은 기회 중 하나입니다.

1. General Questions
2. 일반 질문
3. Open Questions
4. 정해진 답이 없는(Open) 질문
5. Questions about Design Patterns
6. 디자인 패턴 질문
7. Questions about Code Design
8. 코드 설계 질문
9. Questions about languages
10. 프로그래밍 언어 질문
11. Web Questions
12. 웹 질문
13. Databases Questions
14. DB 질문
15. NoSQL Questions
16. NoSQL 질문
17. Code Versioning Questions
18. 코드 버전 관리 질문
19. Concurrency Questions
20. 동시성(Concurrency) 질문
21. Questions about Distributed Systems
22. 분산 시스템 질문
23. Questions about Software Lifecycle and Team Management
24. 소프트웨어 생명 주기와 팀 매니지먼트 질문
25. Questions about logic and algorithms
26. 로직과 알고리즘 질문
27. Questions about Software Architecture
28. 소프트웨어 아키텍쳐 질문
29. Questions about Service Oriented Architecture and Microservices
30. 서비스 기반 아키텍쳐와 마이크로 서비스 질문
31. Questions about Security
32. 보안 질문
33. Bill Gates Style Questions
34. 빌 게이츠 스타일 질문
35. Questions based on snippets of code
36. 예제 코드 조각 기반 질문

####[↑] General Questions:

• Why Functional Programming matters? When should a functional programming language be used?
• 왜 함수형 프로그래밍 언어가 중요한가? 언제 함수형 언어를 사용하면 좋은가?
• What's the difference between design, architecture, functionality and aesthetic? Discuss.
• 설계(Design)와 아키텍쳐(Architecture), 함수성(Functionality)과 심미성(Aesthetic)간의 차이는 무엇인가? 논하시오.
• How do Companies like Microsoft, Google, Opera and Mozilla profit from their browsers?
• MS, 구글, 오페라, 모질라 같은 각 회사는 브라우저로부터 이익을 얻는가?
• Why opening a TCP socket has a large overhead?
• TCP 소켓을 여는데 왜 큰 오버헤드를 갖는가?
• What is Encapsulation important for?
• 캡슐화(Encapsulation)는 무엇에 중요한가?
• What is a real-time system and how is it different from an ordinary system?
• 실시간 시스템이란 무엇이며, 일반 시스템과 다른 점은 무엇인가?
• What's the relationship between real-time languages and heap memory allocation?
• 실시간 언어와 힙 메모리 할당 사이의 관계는 무엇입니까?
• Immutability is the practice of setting values once, at the moment of their creation, and never changing them. How immutability can help writing safer code?
• 불변성(immutability)이란 값(value)을 생성하는 순간에 설정되고 절대 변경되지 않는 관행입니다. 불변성이 어떻게 안전한 코드를 작성하는 데 도움이 되는가?
• Pro and cons of mutable and immutable values.
• 변경 가능한(mutable) 값과 변경 불가능한(immutable) 값의 장단 점을 말하시오.
• What's the Object-Relational impedance mismatch?
• 객체-관계형 임피던스 불일치란 무엇입니까?
• Which principles would you apply to define the size of a cache?
• 캐시의 크기를 정의하는 데 적용 할 원칙은 어떤 것이 있습니까?
• What's the difference between TCP and HTTP?
• TCP와 HTTP의 차이점은 무엇입니까?
• What are the tradeoffs of client-side rendering vs. server-side rendering?
• 클라이언트 렌더링과 서버 렌더링 중 선택에서 절충점(tradeoff)은 무엇입니까?
• How could you develop a reliable communication protocol based on a non-reliable one?
• 신뢰할 수 없는 통신 프로토콜 기반으로 신뢰할 수 있는 통신 프로토콜을 어떻게 개발할 수 있습니까?
• Tony Hoare who invented the null reference once said "I call it my billion-dollar mistake" since it lead to "innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years". Imagine you want to remove the possibility to have null references in your preferred language: how would you achieve this goal? What consequences could this have?
• 널 참조를 발명 한 [Tony Hoare] (https://en.m.wikipedia.org/wiki/Tony_Hoare)는 "나는 그것을 수십억의 실수라고 부른다" 지난 40 년 동안 수십억 달러의 고통과 피해를 입혔을 가능성이있는 취약점들과 시스템 고장 "이라고 지적했다. 원하는 언어로 null 참조를 가질 가능성을 제거한다고 가정 해보십시오. 이 목표를 달성하려면 어떻게해야합니까? 이것이 가져올 결과는 무엇입니까?

####[↑] Open Questions:

• Why do people resist change?
• 왜 사람들은 변화에 저항합니까?
• Explain threads to your grandmother
• 할머니에게 쓰레드(thread)를 설명하십시오.
• As a software engineer you want both to innovate and to be predictable. How those 2 goals can coexist in the same strategy?
• 소프트웨어 엔지니어로서 혁신과 예측이 모두 필요합니다. 이 두 가지 목표가 같은 전략에서 어떻게 공존 할 수 있습니까?
• What makes good code good?
• 좋은 코드가 좋은 이유는 무엇입니까?
• Explain streaming and how you would implement it.
• 스트리밍을 설명하고 구현 방법을 설명하십시오.
• Say your Company gives you one week you can use to improve your and your colleagues' lifes: how would you use that week?
• 귀하의 회사가 당신과 당신 동료의 생활을 향상시키는 데 사용할 수 있는 1 주일을 주겠다고 합니다: 그 주를 어떻게 사용 하시겠습니까?
• What did you learn this week?
• 이번 주에는 무엇을 배웠습니까?
• There is an aesthetic element to all design. The question is, is this aesthetic element your friend or your enemy?
• 모든 디자인에는 미적 요소가 있습니다. 이 미학적 요소는 당신의 친구인가요? 당신의 적인가요?
• List the last 5 books you read.
• 마지막으로 읽은 5권의 책을 나열하세요.
• How would you introduce Continue Delivery in a multi million waterfall shop?
• 수백만 폭포 가게 속에서 지속적인 인도(Continue Delivery)를 어떻게 소개 하겠습니까??
• Let's have a conversation about "Reinventing the wheel", the "Not Invented Here Syndrome" and the "Eating Your Own Food" practice
• "바퀴의 재개발"(Reinventing the wheel), "여기서 개발한 것이 아니다 증후군"(NIH Syndrome) 및 "음식을 먹는 것"(Eating Your Own Food) 연습에 대해 대화 해 봅시다.
• What's the next thing you would automate in your current workflow?
• 현재 워크 플로우에서 다음으로 자동화 할 작업은 무엇입니까?
• Why is writing software difficult? What makes maintaining software hard?
• 소프트웨어를 작성하는 것은 왜 어려운가요? 무엇이 소프트웨어 유지 관리를 어렵게 합니까?
• Would you prefer working on Green Field or Brown Field projects? Why?
• 그린 필드 또는 브라운 필드 프로젝트에서 일하기를 원하십니까? 왜?
• What happens when you type google.com into your browser and press enter?
• 브라우저에 google.com을 입력하고 Enter 키를 누르면 어떻게됩니까?
• What does your computer do when you wait?
• 당신이 기다리는 동안 당신의 컴퓨터는 무엇을 합니까?
• Explain Unicode/Database Transactions to a 5 year old child.
• 유니 코드/데이터베이스 트랜잭션을 5 살짜리 아이에게 설명하십시오.
• Defend the monolithic architecture.
• 모노리식 아키텍처를 방어하세요.
• What does it mean to be a "Professional Developer"?
• "전문 개발자"란 무엇을 의미합니까?
• Is developing software an art, a craftsmanship or an engineering endeavour? Your opinion.
• 소프트웨어를 예술, 장인 정신 또는 공학적 노력으로 개발하고 있습니까?
• "People who like this also like... ". How would you implement this feature in an e-commerce shop?
• "이것을 좋아하는 사람은 ...". 전자 상거래 상점에서 이 기능을 구현하는 방법은 무엇입니까?
• Why are corporations slower than startups in innovating?
• 왜 기업은 스타트업보다 혁신이 느린가?
• Why is it said that cryptography is not something you should try to invent or design yourself?
• 왜 암호화는 당신이 스스로 개발하거나 설계 하려고 노력할 성질의 것이 아니라고 하나요?

####[↑] Questions about Design Patterns:

• Show with an example that global objects are evil.
• Suppose the system you are working on does not support transactionality. How would you implement it from scratch?
• Tell me about the Hollywood Principle.
• About the Law of Demeter (the Principle of Least Knowledge): write a code violating it, then fix it.
• Which are the limits and pitfalls of Active-Record?
• What are the differences between Active-Record and Data-Mapper?
• What is the intent of the Null Object Pattern?
• Why is Composition often better than Inheritance?
• What is an Anti-corruption Layer?
• Could you write a Thread-Safe Singleton class?
• Could you implement Objects in terms of Higher Order Functions, and vice-versa?
• The ability to change implementation without affecting clients is called Data Abstraction. Produce and example violating this property, then fix it.
• Write a snippet of code violating the DRY principle. Then, fix it.
• How would you deal with Dependency Hell?
• Why is goto evil?
• The robustness principle is a general design guideline for software that recommends "Be conservative in what you send, be liberal in what you accept". It is often reworded as "Be a tolerant reader and a careful writer". Would you like to discuss the rationale of this principle?

####[↑] Questions about Code Design:

• What it the tests influence on design?
• What's the difference between cohesion and coupling?
• What is refactoring useful for?
• Are comments in code useful?
• What is the difference between design and architecture?
• Why in TDD tests are written before code?
• C++ supports multiple inheritance, and Java allows a class to implement multiple interfaces. What impact does using these facilities have on orthogonality? Is there a difference in impact between using multiple inheritance and multiple interfaces? Is there a difference between using delegation and using inheritance? [This question is from The Pragmatic Programmer, by Andrew .Hunt and David Thomas]
• Pros and cons of holding domain logic in Stored Procedures.

####[↑] Questions about Languages:

• Tell me the 3 worse defects of your preferred language
• Why is there a rising interest about Functional Programming?
• What is a closure, and what is useful for? What's in common between closures and classes?
• What are generics useful for?
• What are high-order functions? What are they useful for? Write one, in your preferred language.
• Write a loop, then transform it into a recursive function, avoiding mutability. Discuss.
• What does it mean when a language treats functions as first-class citizens?
• Show me an example where an Anonymous Function can be useful
• What is Dynamic Method Dispatch?
• What are namespaces useful for? Invent an alternative.
• Talk about Interoperability between Java and C# (choose 2 other arbitrary languages)
• Why do many software engineers not like Java?
• What makes a good language good and a bad language bad?
• Write two functions, one Referentially Transparent and the other one Referentially Opaque. Discuss.
• Whats the Stack and what's the Heap?
• Why is it important that in a language functions are first class citizen?
• How is Pattern Matching different than Switch clauses?
• Why do some languages have no exceptions by design? What are the pros and cons?
• If Cat is an Animal, is TakeCare<Cat> a TakeCare<Animal>?

####[↑] Questions about Web development:

• Why first-party cookies and third-party cookies are treated so differently?

####[↑] Questions about Databases:

• How would you manage the migration of a project from MySQL to PostgreSQL?
• Why in SQL SELECT * FROM table WHERE field = null does not match records with null field?
• What's ACID (Atomicity, Consistency, Isolation, Durability)?
• How would you manage database schema migrations?
• How is Lazy Loading achieved? When is it useful? What are its pitfalls?
• What's the N+1 problem?
• How would you find the most expensive queries in an application?

####[↑] Questions about NoSQL:

• What is Eventual Consistency?
• About the CAP Theorem, make examples of CP, AP and CA systems.
• How does NoSQL tackle scalability challenges?
• In which case would you use a document database like MongoDB instead of a relational database like MySQL or PostgreSQL?

####[↑] Questions about code versioning:

• Why branching with Mercurial or git is easier than with SVN?
• What are the pros and cons of Distributed Version Control Systems like git over Centralized ones like SVN?
• Could you describe GitHubFLow and GitFlow workflows?
• What's a rebase?
• Why merges are easier with Mercurial and git than with SVN and CVS?

####[↑] Questions about Concurrency:

• Why do we need Concurrency, anyway? Explain.
• Why is testing multithreading / concurrent code so difficult?
• What is a Race Condition? Code an example, using whatever language you like.
• What is a Deadlock? Explain using code.
• What is Process Starvation?
• What is a Wait Free algorithm?

####[↑] Questions about Distributed Systems:

• How to test a distributed system?
• In which case whould you apply asynchronously communication between two systems?
• What are the general pitfalls of Remote Procecure Call?
• If you are building a distributed system for scalability and robustness, what are the different things you'd think of in the case you are working in a closed and secure network environment or in geographically distributed and public system?
• How to manage Fault Tolerance in a Web application? And in a Desktop one?
• How to deal with failures in Distributed Systems?
• Let's talk about the several approaches to Reconciliation after network partitions
• What are the Fallacies of Distributed Computing?
• When would you use Request/Reply and when Publish/Subscribe?

####[↑] Questions about Software Lifecycle and Team Management:

• What is agility?
• How would you deal with Legacy Code?
• I'm the CEO of your Company. Explain me Kanban and convince me to invest on it.
• What is the biggest difference between Agile and Waterfall?
• Being a team manager, how would you deal with the problem of having too many meetings?
• How would you manage a very late project?
• "Individuals and interactions over processes and tools" and "Customer collaboration over contract negotiation" comprise half of the values of the Agile Manifesto. Discuss
• Tell me what decisions would you take if you could be the CTO of your Company.
• Are Program Managers useful?
• Organize a development team using flexible schedules (that is, no imposed working hours) and "Take as you need" vacation policy
• How would you manage a very high turn over and convince developers not to leave the team, without increasing compensation?
• What are the top 3 qualities you look for in colleagues, beyond their code?
• What are the top 3 things you wish non-technical people knew about code?

####[↑] Questions about logic and algorithms:

• Make a FIFO Queue using only LIFO Stacks. Then build a LIFO Stack using only FIFO Queues.
• Write a snippet of code affected by a Stack Overflow
• Write a tail-recursive version of the factorial function
• Using your preferred language, write a REPL that echoes your inputs. Evolve it to make it an RPN calculator.
• How would you design a "defragger" utility?
• Write a program that builds random mazes.
• Write a sample code that produces a memory leak
• Generate a sequence of unique random numbers
• Write a simple Garbage collection system
• Write a basic message broker, using whatever language you like.
• Write a very basic web server. Draw a road map for features to be implemented in the future.
• How would you sort a 10GB file? How would your approach change with a 10TB one?
• Implement the rnd() function.

####[↑] Questions about Software Architecture:

• When is a cache not useful or even dangerous?
• Why does Event-Driven Architecture improve scalability?
• What makes code readable?
• What is the difference between emergent design and evolutionary architecture?
• Scale out vs scale up: how are they different? When to apply one, when the other?
• How to deal with failover and user sessions?
• What is CQRS (Command Query Responsibility Segregation)? How is it different from the oldest Command-Query Separation Principle?
• What is Three-Tier architecture?
• How would you design a software system for scalability?
• What are the strategies to deal with the C10k problem?
• How would you design a decentralized (that is, with no central server) P2P system?
• Why doesn't CGI scale?
• How would you defend the design of your systems against Vendor Lock-in?
• What are the disadvantages of the Publish-Subscribe pattern at scale?
• What's new in CPUs since the 80s, and how does it affect programming?
• In which part of the lifecycle performance should be taken in consideration, and how?
• How could a Denial of Service arise not maliciously but for a design or architectural problem?
• What’s the relationship between Performance and Scalability?
• When is it OK to use tight coupling?
• What characteristic should a system have to be Cloud Ready?
• Does unity of design imply an aristocracy of architects?

####[↑] Questions about Service Oriented Architecture and Microservices:

• Why, in a SOA, long-lived transactions are discorauged and Sagas are suggested instead?
• What are the differences between Soa and Microservices?
• Let's talk about web services versioning, version compatibility and breaking changes.
• What's the difference between a transaction and a compensation operation in a saga, in SOA?
• When is a Microservice too micro?
• What are the pros and cons of MicroService architecture?

####[↑] Questions about Security:

• What's Two Factor Authentication? How would you implement it in an existing web application?

####[↑] Bill Gates Style Questions:

• What would happen if you put a mirror in a scanner?
• Imagine there's a perfect clone of yourself. Imagine that that clone is your boss. Would you like to work for him/her?
• Interview me
• Why are Quora's answers better than Yahoo Answers' ones?
• Defend Cobol against modern languages
• Where will you be in 10 years?
• You are my boss and I'm fired. Inform me.
• I want to refactor a legacy system. You want to rewrite it from scratch. Argument. Then, switch our roles.
• Your boss asks you to lie to the Company. What's your reaction?
• If you could travel back in time, which advice would you give to your younger self?

####[↑] Questions about snippets of code:

• What's the output of this Javascript function?

function hookupevents() {
  for (var i = 0; i < 3; i++) {
    document.getElementById("button" + i)
      .addEventListener("click", function() {
        alert(i);
      });
  }
}

• About Type Erasure, what's the output of this Java snippet, and why?

ArrayList<Integer> li = new ArrayList<Integer>();
ArrayList<Float> lf = new ArrayList<Float>();
if (li.getClass() == lf.getClass()) // evaluates to true
  System.out.println("Equal");

• Can you spot the memory leak?

public class Stack {
    private Object[] elements;
    private int size = 0;
    private static final int DEFAULT_INITIAL_CAPACITY = 16;

    public Stack() {
        elements = new Object[DEFAULT_INITIAL_CAPACITY];
    }

    public void push(Object e) {
        ensureCapacity();
        elements[size++] = e;
    }

    public Object pop() {
        if (size == 0)
            throw new EmptyStackException();
        return elements[--size];
    }

    /**
     * Ensure space for at least one more element, roughly
     * doubling the capacity each time the array needs to grow.
     */
    private void ensureCapacity() {
        if (elements.length == size)
            elements = Arrays.copyOf(elements, 2 * size + 1);
    }
}

• ifs and in general conditional statements lead to procedural and imperative programming. Can you get rid of this switch and make this snippet more object oriented?

public class Formatter {

    private Service service;

    public Formatter(Service service) {
        this.service = service;
    }

    public String doTheJob(String theInput) {
        String response = service.askForPermission();
        switch (response) {
        case "FAIL":
            return "error";
        case "OK":
            return String.format("%s%s", theInput, theInput);
        default:
            return null;
        }
    }
}

• Can you get rid of these ifs and make this snippet of code more object oriented?

public class TheService {
    private final FileHandler fileHandler;
    private final FooRepository fooRepository;

    public TheService(FileHandler fileHandler, FooRepository fooRepository) {
        this.fileHandler = fileHandler;
        this.fooRepository = fooRepository;
    }

    public String Execute(final String file) {

        final String rewrittenUrl = fileHandler.getXmlFileFromFileName(file);
        final String executionId = fileHandler.getExecutionIdFromFileName(file);

        if ((executionId == "") || (rewrittenUrl == "")) {
            return "";
        }

        Foo knownFoo = fooRepository.getFooByXmlFileName(rewrittenUrl);

        if (knownFoo == null) {
            return "";
        }

        return knownFoo.DoThat(file);
    }
}

• How to refactor this code?

function()
{
    HRESULT error = S_OK;

    if(SUCCEEDED(Operation1()))
    {
        if(SUCCEEDED(Operation2()))
        {
            if(SUCCEEDED(Operation3()))
            {
                if(SUCCEEDED(Operation4()))
                {
                }
                else
                {
                    error = OPERATION4FAILED;
                }
            }
            else
            {
                error = OPERATION3FAILED;
            }
        }
        else
        {
            error = OPERATION2FAILED;
        }
    }
    else
    {
        error = OPERATION1FAILED;
    }

    return error;
}