Java

Question 1

An applet

Answer 1

a small program that is intended not to be run on its own, but rather to be embedded inside another application.

Question 2

How to convert JSON string into List of Java object?

Answer 2

mapper.readValue(jsonString, new TypeReference<>(){});

Question 3

for each Map

Answer 3

for(Map.Entry entry: map.entrySet()) {
String key = entry.getKey();
String value = entry.getValue();
}

Question 4

Create class without new in Java

Answer 4

Class ref = Class.forName("CIBuildStatusInfo");
CIBuildStatusInfo obj = (CIBuildStatusInfo) ref.newInstance();

Question 5

BiFunction / Supplier / Consumer ???

Answer 5

// два параметра, возвращает результат
BiFunction {
  R apply(T t, U u);
}
// два параметра, не возвращает результат
BiConsumer  {
  void  accept(T t, U u)
}
// один параметр, возвращает результат
Function {
  R apply(T t);
}
// один параметр, не возвращает результат
Consumer {
  void accept(T t);
}
// Без параметров, возвращает результат
Supplier {
  T get();
}

Question 6

возвращает результат немедленно. Если результат еще не записан, возвращает значение параметра valueIfAbsent. [threads][method]

Answer 6

T getNow(T valueIfAbsent)

Question 7

runAsync / supplyAsync - difference ?

Answer 7

static <u> CompletableFuture<u> supplyAsync(Supplier<u> supplier)</u></u></u>

static CompletableFuture runAsync(Runnable runnable)
</u></u></u>

Question 8

Основной метод. Имеет на входе два фьючерса, результаты которых накапливаются и затем передаются в реакцию, являющейся функцией от двух параметров.

Answer 8

<u> CompletableFuture thenCombine(CompletionStage other, BiFunction fn)
</u>

Question 9

Перехват ошибок исполнения

Answer 9

CompletableFuture exceptionally(Function fn)

Question 10

В этом методе реакция вызывается всегда, независимо от того, заваершился ли данный фьючерс нормально или аварийно. Если фьючерс завершился нормально с результатом r, то в реакцию будут переданы параметры (r, null), если аварийно с исключением ex, то в реакцию будут переданы параметры (null, ex). Результат реакции может быть другого типа, нежели результат данного фьючерса.

Answer 10

<u> CompletableFuture<u> handle(BiFunction fn)</u></u>

</u></u>

Question 11

how to create ExecutorService and ScheduledExecutorService ???

Answer 11

ScheduledExecutorService executorService = Executors
  .newSingleThreadScheduledExecutor();

Question 12

Difference between: scheduleAtFixedRate and scheduleWithFixedDelay ?

Answer 12

FixedRate - will be executed after time delay even if previous task has not been finished yet
FixedDelay - wait till previous task will be finished, wait delay time and start new one

Question 13

@Schedule(cron=”* * * * *”) - tell a bit more about it?

Question 14

restTemplate ??? how to make requests

Answer 14

restTemplate.getForObject(url, List.class);

Question 15

Скільки існує станів потоків?

Answer 15

6: NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED

Question 16

How to create thread and run it?

Answer 16

new Thread(new C()).start();
C should implement Runnable

Question 17

How to give name of thread? (as parameter) we have new MyCustomThread() that implement Runnable

Answer 17

new Thread(new MyCustomThread(), “name”).start()

Question 18

Що таке мьютекс?

Answer 18

взаимное исключение, примитив синхронизации, обеспечивающий защиту определенного обьєкта в потоке от доступа других потоков

Question 19

What is synchronized and how it is used?

Answer 19

So, if we use synchronized in method, it means that only one thread can get access to the method at the same time. When we use without it, every thread has access to it

Question 20

Що таке семафор?

Answer 20

примитив синхронизации работи процесов и потоков в основе которого лежит счетчик

Question 21

What is Callable?

Answer 21

Callable - it is a better version of Runnable. Appears in Java 5.
Callable c = () -> {… should return V}

Question 22

Tell about interface Future

Answer 22

has 5 methods
boolean cancel(boolean mayInterruptIfRunning);
boolean isCancelled();
boolean isDone();
V get();
V get(long timeout, TimeUnit unit);

Question 23

What shouldn’t we forget to do while working with ExecutorService?

Answer 23

executorService.shutdown();

Question 24

Callable and we don’t want to return anything

Answer 24

Callable c = () -> {
…
return null;
}

Question 25

What is TreadPool?

Answer 25

пул тотоков, представляет собой группу робочих потоков которие виолняют задачи. If there is no available thread, our task stands in queue and wait till a thread will be available.

Question 26

Types of Executors???

Answer 26

SingleThreadExecutor
FixedThreadPool(n)
CachedThreadPool
ScheduledExecutor

Cached - 60 seconds and dead

Question 27

Framework Fork / Join

Answer 27

it is a framework for solving problems with using parallel approach “divide and conquer”

Question 28

ComletableFuture vs Future

Answer 28

Future не можна закінчити вручну
Неможливо виконувати багато Future один за одним
Неможливо об’єднувати декілька Future
There is no exception handling

Question 29

java.util.function

Answer 29

Consumer return void
Function return R
Supplier return T
BiFunction return R
BiConsumer

Question 30

Exception handling in ComletalbeFuture

Answer 30

handle, whenComplete, exceptionally / exceptionallyCompose

Question 31

List list = new ArrayList();
default value?

Answer 31

Object

Question 32

usual names for generic types in java?

Answer 32

The most commonly used type parameter names are:
E — Element
K — Key
N — Number
T — Type
V — Value
S, U, V etc. — second, third, and fourth types

Question 33

List - why is it wrong?

Answer 33

we can’t use primitive types in generics

Question 34

how to create a method with generic parameter without generic class declaration in Java?

Answer 34

public int getCount(List elements) {
return elements.size();
}

Question 35

what is wildcard in Java?

Answer 35

wildcard character (?) is used to indicate unknown type

Question 36

What is cascade=CascadeType.ALL in Spring JPA?

Answer 36

it means all changes that were applied to one table, reflect on another (for relations oneToMany and manyToOne)