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Full-stack Developer Interview Questions and Answers

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[⬆] Architecture:

Rule Description
Single responsibility principle A module should be responsible to one, and only one, actor.
Open/closed principle A software artifact should be open for extension but closed for modification.
Liskov substitution principle It should be possible to substitute base class with derived class.
Interface segregation principle Many client-specific interfaces are better than one general-purpose interface.
Dependency inversion principle Depend upon Abstractions but not on concretions. This means that each module should be separated from other using an abstract layer which binds them together. Source code dependency points in the opposite direction compared to the flow of control.

[⬆] Concurrency:

  • What is deadlock, livelock? (Deadlock is a situation in which two or more competing actions are each waiting for the other to finish, and thus neither ever does. A livelock is similar to a deadlock, except that the states of the processes involved in the livelock constantly change with regard to one another, none progressing.)

  • Deadlock Prevention. (prevention, detection, avoidance (Mutex hierarchy), and recovery)

  • Deadlock Avoidance. (Deadlock is a situation that occurs in Operating System when any Process enters a waiting state because another waiting process is holding the demanded resource.)

  • What is starvation? (a problem encountered in concurrent computing where a process is perpetually denied necessary resources to process its work)

  • What is race condition? (Behavior of software system where the output is dependent on the sequence or timing of other uncontrollable events)

  • What is happens-before relation?

  • What is thread contention? (Contention is simply when two threads try to access either the same resource or related resources in such a way that at least one of the contending threads runs more slowly than it would if the other thread(s) were not running). Contention occurs when multiple threads try to acquire a lock at the same time

  • What is a thread-safe function? (Can be safely invoked by multiple threads at the same time)

  • Publish/Subscribe pattern

  • What is 2-phase locking? (Growing phase, shrinking phase. Guarantees serializablity for transactions, doesn't prevent deadlock).

  • What is the difference between thread and process? (Threads (of the same process) run in a shared memory space, while processes run in separate memory spaces)

  • What is false sharing, cache pollution, cache miss, thread affinity, ABA-problem, speculative execution?

  • What is a

    • obstruction-free - if all other threads are paused, then any given thread will complete its operation in a bounded number of steps
    • lock-free - if multiple threads are operating on a data structure, then after a bounded number of steps one of them will complete its operation
    • wait-free - every thread operating on a data structure will complete its operation in a bounded number of steps, even if other threads are also operating on the data structure


  • What is sequential consistency? (The result of any execution is the same as if the operations of all the processors were executed in some sequential order, and the operations of each individual processor appear in this sequence in the order specified by its program).

  • What is a memory barrier? (A memory barrier, also known as a membar, memory fence or fence instruction, is a type of barrier instruction that causes a CPU or compiler to enforce an ordering constraint on memory operations issued before and after the barrier instruction)

  • Synchonization aids in Java

    • CountDownLatch
    • CyclicBarrier
    • Phaser
    • ReentrantLock
    • Exchanger
    • Semaphore
    • LinkedTransferQueue
  • What is data race? (When a program contains two conflicting accesses that are not ordered by a happens-before relationship, it is said to contain a data race. Two accesses to (reads of or writes to) the same variable are said to be conflicting if at least one of the accesses is a write. But see this)

  • Java memory model

    • A program is correctly synchronized if and only if all sequentially consistent executions are free of data races
    • Correctly synchronized programs have sequentially consistent semantics. If a program is correctly synchronized, then all executions of the program will appear to be sequentially consistent
    • Causality requirement for incorrectly synchronized programs: link
  • What is monitor in Java? (Each object in Java is associated with a monitor, which a thread can lock or unlock)

  • What is safe publication?

  • What is wait/notify?

  • Amdahl's law? (Speedup = 1 / (1 - p + p / n))

  • Dining philosophers problem (Resource hierarchy (first take lower-indexed fork), arbitrator, communication (dirty/clean forks)).

  • Produces/consumer problem.

  • Readers/writers problem.

  • Transactional memory

  • Coroutine

[⬆] Java:

  • PhantomReference, WeakReference, SoftReference, finalize(), ReferenceQueue.
  • How to correctly stop a thread? (Thread.interrupt())
  • What is Spring? (Spring Framework is an application container for Java that supplies many useful features, such as Inversion of Control, Dependency Injection, abstract data access, transaction management, and more)
    • Spring is a framework for dependency injection: a design pattern that allows the developer to build very decoupled systems by injecting dependencies into classes.
    • It elegantly wraps Java libraries and makes then much easier to use in your application.
    • Included in the framework are implementations of commonly used patterns such as REST and MVC web framework which are predominately use by in web applications.
  • What is Spring-Boot?
  • What is Hibernate and JPA (Caches, lazy-loading)?
  • Garbage collection. (G1, Young/Old generation collectors combination examples: PS Scavenge/PS MarkSweep, Copy/MarkSweepCompact)
  • How to write benchmarks? (jmh)
  • What are Java 9 modularity?
  • What is OSGI? (Specification describes a modular system and a service platform for the Java programming language that implements a complete and dynamic component model. Each bundle has its own classpath. Dependency hell avoidance. META-INF/MANIFEST.MF contains OSGI-info)
  • Serializable / Externalizable
  • What is a servlet (versions of servlet api, Servlet 4.0)?
  • What is a servlet filter? How to implement GZipFilter? (ResponseWrapper)
  • What is generics and PECS (producer extends and consumer super)?
  • What is the difference between <?>, <Object>, <? extends Object> and no generic type? link1 link2
  • Explain method signature for Collections.max(...), Collections.fill(...), Collections.copy(...), Collections.sort(...)
  • Why are arrays covariant but generics are invariant? link
  • Performance Diagnostic Methodology

[⬆] General Questions:

  • Polymorphism (Variable of type Shape could refer to an object of type Square, Circle... Ability of a function to handle objects of many types)
  • Encapsulation (Packing of data and functions into a single component)
  • Virtual function (Overridable function)
  • Virtual method table
  • Dynamic binding (Actual method implementation invoked is determined at run time based on the class of the object, not the type of the variable or expression)
  • How does garbage collector work? (Mark and sweep: mark: traverse object graph starting from root objects, sweep: garbage collect unmarked objects. Optimizations: young/old generations, incremental mark and sweep)
  • Tail recursion (A tail call is a subroutine call performed as the final action of a procedure)
  • Semantic versioning

[⬆] WEB:

[⬆] SQL:

  • SQL join types (inner join, left/right outer join, full outer join, cross join) Join types)
  • SQL normal forms
    1. The domain of each attribute contains only atomic values, and the value of each attribute contains only a single value from that domain
    2. No non-prime attribute in the table is functionally dependent on a proper subset of any candidate key
    3. Every non-prime attribute is non-transitively dependent on every candidate key in the table. BCNF.Every non-trivial functional dependency in the table is a dependency on a superkey.)
  • Isolation levels and Anomalies
Isolation_level\Anomaly Lost_update (because of rollback) Dirty_read Non_repeatable_reads second_lost_update Phantoms Write_skew
Read Uncommitted - may occur may occur may occur may occur
Read Committed - - may occur may occur may occur
Repeatable Read - - - may occur may occur
Snapshot - - - - may occur
Serializable - - - - -

[⬆] NoSQL:

  • Types of NoSQL databases?
    • Document Stores (MongoDB, Couchbase)
    • Key-Value Stores (Redis, Volgemort)
    • Column Stores (Cassandra)
    • Graph Stores (Neo4j, Giraph)

[⬆] Transactions:

[⬆] Scalability:

  • Horizontal and vertical scaling.
  • How to scale database? (Data partitioning, sharding(vertical/horizontal), replication(master-slave, master-master)).
  • Denormalization.
  • What is synchronous multimaster replication? (Each server can accept write requests, and modified data is transmitted from the original server to every other server before each transaction commits)
  • What is asynchronous multimaster replication? (Each server works independently, and periodically communicates with the other servers to identify conflicting transactions. The conflicts can be resolved by users or conflict resolution rules)
  • When to use messaging queue?
  • MongoDB, Redis.
  • Hadoop basics.

[⬆] Load balancing:

  • sticky/non-sticky sessions
  • Sticky sessions vs storing sessions in Redis.

[⬆] Cloud computing:

[⬆] Distributed:

1 Read-write registers
2 Test-and-set, swap, fetch-and-add, queue, stack
⋮ ⋮
∞ Augmented queue, compare-and-swap, sticky byte

[⬆] Cache:

  • What is write-through and write-behind caching? (write-through (synchronous), write-behind (asynchronous))
  • HTTP cache options?

[⬆] Networking:

  • OSI model (Physical, Data link, Network, Transport, Session, Presentation, Application)
  • Multithreading vs select
  • Switch, hub, router
  • TCP congestion
  • TCP back-pressure

[⬆] Operating system:

[⬆] Compilers:

[⬆] C++:

  • C++ standard

  • Memory model

  • Data race. When an evaluation of an expression writes to a memory location and another evaluation reads or modifies the same memory location, the expressions are said to conflict. A program that has two conflicting evaluations has a data race unless

    • both evaluations execute on the same thread or in the same signal handler, or
    • both conflicting evaluations are atomic operations (see std::atomic), or
    • one of the conflicting evaluations happens-before another (see std::memory_order)

    If a data race occurs, the behavior of the program is undefined.

  • SFINAE 1

  • [PImpl] https://en.cppreference.com/w/cpp/language/pimpl

[⬆] Javascript:

  • this keyword
  • How prototypes work?
  • inheritance
  • differences between == and === (http://dorey.github.io/JavaScript-Equality-Table/)
  • closures
  • recursion
  • What is MVC, MVP, MVVM?
  • What is promise?
  • What is event bubbling and capturing? (target.addEventListener(type, listener[, useCapture]))
  • What is AMD(Asynchronous Module Design) and CommonJS?
  • What is jQuery?

[⬆] Python:

[⬆] Go:

[⬆] Codewriting:

  • Implement binary search
int binarySearch(int[] a, int fromInclusive, int toExclusive, int key) {
    int low = fromInclusive;
    int high = toExclusive - 1;
    while (low <= high) {
        int mid = (low + high) >>> 1;
        int midVal = a[mid];
        if (midVal < key)
            low = mid + 1;
        else if (midVal > key)
            high = mid - 1;
            return mid; // key found
    return -(low + 1); // key not found
  • Implement quick sort
void qSort(int[] a, int fromInclusive, int toInclusive) {
    int i = fromInclusive;
    int j = toInclusive;
    if (i >= j) return;
    int separator = a[i + random.nextInt(j - i + 1)];
    do {
        while (a[i] < separator) ++i;
        while (a[j] > separator) --j;
        if (i > j) break;
        int t = a[i];
        a[i] = a[j];
        a[j] = t;
    } while (i <= j);
    qSort(a, fromInclusive, j);
    qSort(a, i, toInclusive);

[⬆] Functional programming:

[⬆] Reactive programming:

[⬆] Git:

[⬆] DevOps:

  • What is Blue-green Deployment, Canary release, A/B testing? link
  • What is Docker?

[⬆] QA:

  • What is unit test? (A test that purely tests a single unit of functionality)
  • What is component test?
  • What is integration test? (Examine several parts of a system to make sure that when integrated, these parts behave as expected)
  • What is user acceptance test? BDD?
  • Unit tests advantages?
  • Types of tests: acceptance testing, functional testing, smoke testing, regression testing, unit testing, integration testing, stress testing, (Load, Performance, Sanity, Stability, Security, Feature, Progression, Installation, Business).
  • Differences between stub and mock? (A stub is a test double with preprogrammed behavior. Mocks are stubs with preprogrammed expectations)
  • Selenium tests and webdriver.
  • How to test multithreading code?
  • What is Consumer Driven Contract? link
  • Types of tests

[⬆] Agile:

[⬆] Algorithms:

  • What Ο(n), Ω(n), Θ(n)?
  • What is NP, NP-completeness, NP-hardness with examples?

[⬆] Other:

  • How to find memory leak. (Memory snapshot diff).
  • Profiling: sampling and instrumentation.
  • Regular expressions. (Examples)
  • What are your goals to work in our company? (3 categories: professional, financial, social)
  • What is virtualization?
  • What is total/partial order?
  • How to work with legacy code? (http://programmers.stackexchange.com/a/122024)

[⬆] Machine learning:


[⬆] Big Data:

[⬆] Image processing:

[⬆] Cryptography:

select 2 primes: p,q
n = p*q
phi(n) = (p-1)*(q-1)
select 1<e<phi(n), gcd(e,phi(n))=1
d=e^-1 mod phi(n)
(e,n) - public key
(d,n) - private key
c = m^e mod n
m = c^d mod n = m^(e*d) mod n = m^(e*d mod phi(n)) mod n = m

[⬆] Security:

  • What is OpenID and OAuth2.0 and OpenID Connect?
  • Four main actors in an OAuth system (clients, resource owners, authorization servers, and protected resources)
  • What is access_token, refresh_token, SAML token, JWT token?
  • Sticky session vs Session Replication.
  • What is hash salt?
  • What is Federated Authentication ?
  • What is CSP and SRI hash ?
  • What is Clickjacking and Cursorjacking ? How to prevent it ?

[⬆] Android:

[⬆] Books:

C++ programming
Java programming
Concurrent programming
Machine Learning
Digital Signal Processing
Digital Image Processing
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