Reactor Core Reference Guide

https://projectreactor.io/docs/core/release/reference/
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### Create a replay sink with Sinks.many().replay().all()

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/sinks.html

Creates a Sinks.Many that replays all pushed data to new subscribers. This is the starting point for the multi-threaded emission examples.

```java
Sinks.Many<Integer> replaySink = Sinks.many().replay().all();
```

--------------------------------

### Output of custom request example

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/simple-ways-to-create-a-flux-or-mono-and-subscribe-to-it.html

This is the printed output from the preceding BaseSubscriber example. It shows the request of 1 and the cancellation message after receiving the first element.

```java
request of 1
Cancelling after having received 1
```

--------------------------------

### Cold Flux example with two subscribers

Source: https://projectreactor.io/docs/core/release/reference/advancedFeatures/reactor-hotCold.html

This example demonstrates a cold Flux. Each subscriber triggers the data generation process, so both subscribers receive all four colors. The output shows each subscriber receiving the full sequence.

```java
Flux<String> source = Flux.fromIterable(Arrays.asList("blue", "green", "orange", "purple"))
                          .map(String::toUpperCase);

source.subscribe(d -> System.out.println("Subscriber 1: "+d));
source.subscribe(d -> System.out.println("Subscriber 2: "+d));
```

```java
Subscriber 1: BLUE
Subscriber 1: GREEN
Subscriber 1: ORANGE
Subscriber 1: PURPLE
Subscriber 2: BLUE
Subscriber 2: GREEN
Subscriber 2: ORANGE
Subscriber 2: PURPLE
```

--------------------------------

### Example chain with transforms and blockLast

Source: https://projectreactor.io/docs/core/release/reference/debugging.html

An example chain that demonstrates a scenario where the error observation section would be more informative. It shows a sequence of transforms and a blockLast call.

```java
FakeRepository.findAllUserByName(Flux.just("pedro", "simon", "stephane"))
              .transform(FakeUtils1.applyFilters)
              .transform(FakeUtils2.enrichUser)
              .blockLast();
```

--------------------------------

### Output of handle example

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/programmatically-creating-sequence.html

The output printed by the handle example, showing the letters M, I, T.

```java
M
I
T
```

--------------------------------

### Callback Hell Example: Fetching User Favorites

Source: https://projectreactor.io/docs/core/release/reference/reactiveProgramming.html

This example shows the complexity of composing callbacks, where nested callbacks are used to fetch user favorites, their details, and suggestions. It demonstrates the 'Callback Hell' problem, making the code difficult to read and maintain. The code uses UiUtils to submit UI updates and handles errors with error popups.

```java
userService.getFavorites(userId, new Callback<List<String>>() { (1)
  public void onSuccess(List<String> list) { (2)
    if (list.isEmpty()) { (3)
      suggestionService.getSuggestions(new Callback<List<Favorite>>() {
        public void onSuccess(List<Favorite> list) { (4)
          UiUtils.submitOnUiThread(() -> { (5)
            list.stream()
                .limit(5)
                .forEach(uiList::show); (6)
            });
        }

        public void onError(Throwable error) { (7)
          UiUtils.errorPopup(error);
        }
      });
    } else {
      list.stream() (8)
          .limit(5)
          .forEach(favId -> favoriteService.getDetails(favId, (9)
            new Callback<Favorite>() {
              public void onSuccess(Favorite details) {
                UiUtils.submitOnUiThread(() -> uiList.show(details));
              }

              public void onError(Throwable error) {
                UiUtils.errorPopup(error);
              }
            }
          ));
    }
  }

  public void onError(Throwable error) {
    UiUtils.errorPopup(error);
  }
});
```

--------------------------------

### StepVerifier.withVirtualTime with Mono.delay

Source: https://projectreactor.io/docs/core/release/reference/testing.html

Starts a virtual time test for a time-based operator. The Supplier must lazily create the Flux or Mono after the virtual time scheduler is activated. This example sets up a one-day delay.

```java
StepVerifier.withVirtualTime(() -> Mono.delay(Duration.ofDays(1)))
//... continue expectations here
```

--------------------------------

### Initialize ReactorDebugAgent in main method

Source: https://projectreactor.io/docs/core/release/reference/debugging.html

Shows the recommended placement of ReactorDebugAgent.init() at the start of the main method, before running the application.

```java
public static void main(String[] args) {
    ReactorDebugAgent.init();
    SpringApplication.run(Application.class, args);
}
```

--------------------------------

### Read and write to Context with Mono.deferContextual and contextWrite

Source: https://projectreactor.io/docs/core/release/reference/advancedFeatures/context.html

Shows how to write a value to the Context using contextWrite and read it with deferContextual. The example uses a key "message" and expects the output "Hello World".

```java
String key = "message";
Mono<String> r = Mono.just("Hello")
    .flatMap(s -> Mono.deferContextual(ctx ->
         Mono.just(s + " " + ctx.get(key))))
    .contextWrite(ctx -> ctx.put(key, "World"));

StepVerifier.create(r)
            .expectNext("Hello World")
            .verifyComplete();
```

--------------------------------

### Output without runOn

Source: https://projectreactor.io/docs/core/release/reference/advancedFeatures/advanced-parallelizing-parralelflux.html

Output of the first example (without runOn) showing all items processed on the main thread.

```java
main -> 1
main -> 2
main -> 3
main -> 4
main -> 5
main -> 6
main -> 7
main -> 8
main -> 9
main -> 10
```

--------------------------------

### Hot Flux example using Sinks.Many

Source: https://projectreactor.io/docs/core/release/reference/advancedFeatures/reactor-hotCold.html

This example demonstrates a hot Flux using Sinks.unsafe().many().multicast().directBestEffort(). Subscriber 1 receives all elements, while Subscriber 2, subscribing later, only receives elements emitted after its subscription. The output shows the difference.

```java
Sinks.Many<String> hotSource = Sinks.unsafe().many().multicast().directBestEffort();

Flux<String> hotFlux = hotSource.asFlux().map(String::toUpperCase);

hotFlux.subscribe(d -> System.out.println("Subscriber 1 to Hot Source: "+d));

hotSource.emitNext("blue", FAIL_FAST); (1)
hotSource.tryEmitNext("green").orThrow(); (2)

hotFlux.subscribe(d -> System.out.println("Subscriber 2 to Hot Source: "+d));

hotSource.emitNext("orange", FAIL_FAST);
hotSource.emitNext("purple", FAIL_FAST);
hotSource.emitComplete(FAIL_FAST);
```

```java
Subscriber 1 to Hot Source: BLUE
Subscriber 1 to Hot Source: GREEN
Subscriber 1 to Hot Source: ORANGE
Subscriber 2 to Hot Source: ORANGE
Subscriber 1 to Hot Source: PURPLE
Subscriber 2 to Hot Source: PURPLE
```

--------------------------------

### Output with runOn

Source: https://projectreactor.io/docs/core/release/reference/advancedFeatures/advanced-parallelizing-parralelflux.html

Output of the second example (with runOn) showing items processed on two parallel threads.

```java
parallel-1 -> 1
parallel-2 -> 2
parallel-1 -> 3
parallel-2 -> 4
parallel-1 -> 5
parallel-2 -> 6
parallel-1 -> 7
parallel-1 -> 9
parallel-2 -> 8
parallel-2 -> 10
```

--------------------------------

### subscribeOn example with parallel Scheduler

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/schedulers.html

Creates a Scheduler with four threads, then uses subscribeOn to shift the entire subscription and request signals to a Scheduler thread. Both map operators and the print run on the same Scheduler thread.

```java
Scheduler s = Schedulers.newParallel("parallel-scheduler", 4); (1)

final Flux<String> flux = Flux
    .range(1, 2)
    .map(i -> 10 + i)  (2)
    .subscribeOn(s)  (3)
    .map(i -> "value " + i);  (4)

new Thread(() -> flux.subscribe(System.out::println));  (5)
```

--------------------------------

### Expected output of exponential backoff example

Source: https://projectreactor.io/docs/core/release/reference/faq.html

Shows the console output when the exponential backoff example is subscribed to. It fails and terminates after printing the error and retry times with increasing delays (approximately 100ms, 200ms, 400ms).

```java
java.lang.IllegalStateException: boom at 00:00:00.0
retried at 00:00:00.101, attempt 0 (1)
java.lang.IllegalStateException: boom at 00:00:00.101
retried at 00:00:00.304, attempt 1 (2)
java.lang.IllegalStateException: boom at 00:00:00.304
retried at 00:00:00.702, attempt 2 (3)
java.lang.IllegalStateException: boom at 00:00:00.702
```

--------------------------------

### CompletableFuture asynchronous combination example

Source: https://projectreactor.io/docs/core/release/reference/reactiveProgramming.html

Shows how to asynchronously fetch IDs, then for each ID fetch name and stats, combine them, and wait for all tasks to complete using CompletableFuture.allOf and join(). The final result is asserted with expected values.

```java
CompletableFuture<List<String>> ids = ifhIds(); (1)

CompletableFuture<List<String>> result = ids.thenComposeAsync(l -> { (2)
	Stream<CompletableFuture<String>> zip =
			l.stream().map(i -> { (3)
				CompletableFuture<String> nameTask = ifhName(i); (4)
				CompletableFuture<Integer> statTask = ifhStat(i); (5)

				return nameTask.thenCombineAsync(statTask, (name, stat) -> "Name " + name + " has stats " + stat); (6)
			});
	List<CompletableFuture<String>> combinationList = zip.collect(Collectors.toList()); (7)
	CompletableFuture<String>[] combinationArray = combinationList.toArray(new CompletableFuture[combinationList.size()]);

	CompletableFuture<Void> allDone = CompletableFuture.allOf(combinationArray); (8)
	return allDone.thenApply(v -> combinationList.stream()
			.map(CompletableFuture::join) (9)
			.collect(Collectors.toList()));
});

List<String> results = result.join(); (10)
assertThat(results).contains(
		"Name NameJoe has stats 103",
		"Name NameBart has stats 104",
		"Name NameHenry has stats 105",
		"Name NameNicole has stats 106",
		"Name NameABSLAJNFOAJNFOANFANSF has stats 121");
```

--------------------------------

### Reactive try-with-resource using() example

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/error-handling.html

Uses Flux.using to generate a resource, process it, and clean up. The third lambda is called on termination or cancellation.

```java
Flux<String> flux =
Flux.using(
        () -> disposableInstance, (1)
        disposable -> Flux.just(disposable.toString()), (2)
        Disposable::dispose (3)
);
```

--------------------------------

### Operator chaining: best practice with chaining

Source: https://projectreactor.io/docs/core/release/reference/faq.html

This example shows the preferred way of using operators by chaining calls directly, which is simpler and avoids the need to reassign the variable.

```java
Flux.just("something", "chain")
    .map(secret -> secret.replaceAll(".", "*"))
    .subscribe(next -> System.out.println("Received: " + next));
```

--------------------------------

### Flux.interval with retry(1) to show re-subscription

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/error-handling.html

Appends retry(1) to the interval example, causing a re-subscription to the original Flux after the error. The output shows a new interval starting from tick 0, and then the error propagates after the second failure. Uses elapsed to show timing and subscribes with an error consumer.

```java
Flux.interval(Duration.ofMillis(250))
    .map(input -> {
        if (input < 3) return "tick " + input;
        throw new RuntimeException("boom");
    })
    .retry(1)
    .elapsed() (1)
    .subscribe(System.out::println, System.err::println); (2)

Thread.sleep(2100); (3)
```

```java
259,tick 0
249,tick 1
251,tick 2
506,tick 0 (1)
248,tick 1
253,tick 2
java.lang.RuntimeException: boom
```

--------------------------------

### Basic Context write and read with contextWrite and deferContextual

Source: https://projectreactor.io/docs/core/release/reference/advancedFeatures/context.html

Shows the basic usage of contextWrite to put a value and deferContextual to read it. The execution order is bottom-up: contextWrite is executed first even though it appears last in the chain. The resulting Mono emits 'Hello World'.

```java
String key = "message";
Mono<String> r = Mono.just("Hello")
    .flatMap(s -> Mono.deferContextual(ctx ->
         Mono.just(s + " " + ctx.get(key)))) (2)
    .contextWrite(ctx -> ctx.put(key, "World")); (1)

StepVerifier.create(r)
            .expectNext("Hello World") (3)
            .verifyComplete();
```

--------------------------------

### Mono#and

Source: https://projectreactor.io/docs/core/release/reference/apdx-operatorChoice.html

Combines this Mono with any source, producing a Mono<Void> that completes when both complete.

```APIDOC
## Mono#and

### Description
Combines this Mono with any source, producing a Mono<Void> that completes when both complete.

### Method
and(Publisher<?> other)

### Parameters
- **other** (Publisher<?>) - Required - The other publisher to combine with.

### Returns
Mono<Void> - A Mono that completes when both sources complete.
```

--------------------------------

### Flux.range(int, int)

Source: https://projectreactor.io/docs/core/release/reference/apdx-operatorChoice.html

Creates a Flux that emits a range of integers starting from start and incrementing by 1.

```APIDOC
## Flux.range(int, int)

### Description
Creates a Flux that emits a range of integers starting from start and incrementing by 1.

### Method
range

### Signature
`Flux<Integer> range(int start, int count)`

### Parameters
- **start** (int) - Required - The first integer to emit.
- **count** (int) - Required - The number of integers to emit.

### Returns
A new `Flux` that emits the range of integers.

### Example
```java
Flux<Integer> flux = Flux.range(1, 3); // emits 1, 2, 3
```
```

--------------------------------

### Output of incorrect chaining example

Source: https://projectreactor.io/docs/core/release/reference/faq.html

This is the output produced by the incorrect example where the map result is not assigned. It prints the original values.

```java
Received: something
Received: chain
```

--------------------------------

### Using PublisherProbe to test empty path

Source: https://projectreactor.io/docs/core/release/reference/testing.html

Creates a probe for an empty sequence, uses it in place of Mono<Void>, and asserts subscription, request, and no cancellation.

```java
@Test
public void testCommandEmptyPathIsUsed() {
    PublisherProbe<Void> probe = PublisherProbe.empty(); (1)

    StepVerifier.create(processOrFallback(Mono.empty(), probe.mono())) (2)
                .verifyComplete();

    probe.assertWasSubscribed(); (3)
    probe.assertWasRequested(); (4)
    probe.assertWasNotCancelled(); (5)
}
```

--------------------------------

### Output of correct chaining examples

Source: https://projectreactor.io/docs/core/release/reference/faq.html

This is the output produced by the correct examples where the map result is assigned or chained. It prints the transformed values.

```java
Received: *********
Received: *****
```

--------------------------------

### Operator chaining: correct example with reassignment

Source: https://projectreactor.io/docs/core/release/reference/faq.html

This example correctly assigns the result of map back to the flux variable, so the subscription prints the transformed values.

```java
Flux<String> flux = Flux.just("something", "chain");
flux = flux.map(secret -> secret.replaceAll(".", "*"));
flux.subscribe(next -> System.out.println("Received: " + next));
```

--------------------------------

### Mono#when

Source: https://projectreactor.io/docs/core/release/reference/apdx-operatorChoice.html

Combines multiple sources into a Mono<Void> that completes when all complete.

```APIDOC
## Mono#when

### Description
Combines multiple sources into a Mono<Void> that completes when all complete.

### Method
when(Iterable<? extends Publisher<?>> sources)

### Parameters
- **sources** (Iterable<? extends Publisher<?>>) - Required - The sources to combine.

### Returns
Mono<Void> - A Mono that completes when all sources complete.
```

--------------------------------

### contextCapture Operator Example

Source: https://projectreactor.io/docs/core/release/reference/advanced-contextPropagation.html

Captures ThreadLocal values at subscription time using contextCapture. The example shows that in default mode, the ThreadLocal is not propagated, but in automatic mode it is.

```java
// assuming TL is known to Context-Propagation as key TLKEY.
static final ThreadLocal<String> TL = new ThreadLocal<>();

// in the main Thread, TL is set to "HELLO"
TL.set("HELLO");

Mono.deferContextual(ctx ->
  Mono.delay(Duration.ofSeconds(1))
      // we're now in another thread, TL is not explicitly set
      .map(v -> "delayed ctx[" + TLKEY + "]=" + ctx.getOrDefault(TLKEY, "not found") + ", TL=" + TL.get()))
.contextCapture() // can be skipped in automatic mode when a blocking operator follows
.block(); // returns "delayed ctx[TLKEY]=HELLO, TL=null" in default mode
          // returns "delayed ctx[TLKEY]=HELLO, TL=HELLO" in automatic mode
```

--------------------------------

### contextWrite Operator Example

Source: https://projectreactor.io/docs/core/release/reference/advanced-contextPropagation.html

Stores a value in the Context at subscription time using contextWrite. The example shows that in default mode, the ThreadLocal is not propagated, but in automatic mode it is.

```java
// assuming TL is known to Context-Propagation as key TLKEY.
static final ThreadLocal<String> TL = new ThreadLocal<>();

// in the main Thread, TL is not set

Mono.deferContextual(ctx ->
  Mono.delay(Duration.ofSeconds(1))
      // we're now in another thread, TL is not explicitly set
      .map(v -> "delayed ctx[" + TLKEY + "]=" + ctx.getOrDefault(TLKEY, "not found") + ", TL=" + TL.get()))
.contextWrite(ctx -> ctx.put(TLKEY, "HELLO"))
.block(); // returns "delayed ctx[TLKEY]=HELLO, TL=null" in default mode
          // returns "delayed ctx[TLKEY]=HELLO, TL=HELLO" in automatic mode
```

--------------------------------

### Mono.then(mono)

Source: https://projectreactor.io/docs/core/release/reference/apdx-operatorChoice.html

Switches to another Mono after the source Mono completes.

```APIDOC
## Mono.then(mono)

### Description
Switches to another Mono after the source Mono completes.

### Applicable Types
- Mono

### Signature
- `Mono.then(Mono<? extends V> other)`

### Parameters
- `other` (Mono<? extends V>) - Required - The Mono to switch to after the source completes.

### Returns
- A new Mono that emits the value from the other Mono.

### API Reference
- [Mono.then(mono)](https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html#then-reactor.core.publisher.Mono-)
```

--------------------------------

### Flux#sample(Publisher)

Source: https://projectreactor.io/docs/core/release/reference/apdx-operatorChoice.html

Samples items by a publisher-based window, emitting the last element in each window triggered by the publisher.

```APIDOC
## Flux#sample(Publisher)

### Description
Samples items by a publisher-based window, emitting the last element in each window triggered by the publisher.

### Method
sample

### Signature
Flux<T> sample(Publisher<?> sampler)

### Parameters
- **sampler** (Publisher<?>) - Required - The publisher that defines the sampling windows.

### Returns
A Flux that emits the last element of each sampling window.

### Reference
[Flux#sample(Publisher)](https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Flux.html#sample-org.reactivestreams.Publisher-)
```

--------------------------------

### Operator chaining: incorrect example without reassignment

Source: https://projectreactor.io/docs/core/release/reference/faq.html

This example shows the mistake of not assigning the result of map back to the flux variable. The map operator returns a new instance, so the original flux remains unchanged, and the subscription prints the original values.

```java
Flux<String> flux = Flux.just("something", "chain");
flux.map(secret -> secret.replaceAll(".", "*")); (1)
flux.subscribe(next -> System.out.println("Received: " + next));
```

--------------------------------

### publishOn example with parallel Scheduler

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/schedulers.html

Creates a Scheduler with four threads, then uses publishOn to switch the execution context for downstream operators. The first map runs on the subscribing thread, while the second map and the print run on a thread from the Scheduler.

```java
Scheduler s = Schedulers.newParallel("parallel-scheduler", 4); (1)

final Flux<String> flux = Flux
    .range(1, 2)
    .map(i -> 10 + i)  (2)
    .publishOn(s)  (3)
    .map(i -> "value " + i);  (4)

new Thread(() -> flux.subscribe(System.out::println));  (5)
```

--------------------------------

### Imperative catch and rethrow as BusinessException

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/error-handling.html

Imperative example of catching a Throwable and rethrowing it as a BusinessException.

```java
try {
  return callExternalService(k);
}
catch (Throwable error) {
  throw new BusinessException("oops, SLA exceeded", error);
}
```

--------------------------------

### ConnectableFlux with publish() and connect()

Source: https://projectreactor.io/docs/core/release/reference/advancedFeatures/advanced-broadcast-multiple-subscribers-connectableflux.html

Creates a ConnectableFlux using publish(), subscribes two subscribers, then manually triggers the connection with connect(). The output shows that the source is only subscribed after connect() is called, and each value is emitted to both subscribers.

```java
Flux<Integer> source = Flux.range(1, 3)
                           .doOnSubscribe(s -> System.out.println("subscribed to source"));

ConnectableFlux<Integer> co = source.publish();

co.subscribe(System.out::println, e -> {}, () -> {});
co.subscribe(System.out::println, e -> {}, () -> {});

System.out.println("done subscribing");
Thread.sleep(500);
System.out.println("will now connect");

co.connect();
```

```java
done subscribing
will now connect
subscribed to source
1
1
2
2
3
3
```

--------------------------------

### Subscribe with no arguments

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/simple-ways-to-create-a-flux-or-mono-and-subscribe-to-it.html

Sets up a Flux that produces three values and subscribes in the simplest way. Produces no visible output.

```java
Flux<Integer> ints = Flux.range(1, 3); (1)
ints.subscribe(); (2)
```

--------------------------------

### Disposable resource for using()

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/error-handling.html

Defines a Disposable instance that sets an AtomicBoolean on dispose. Used as the resource for the using() example.

```java
AtomicBoolean isDisposed = new AtomicBoolean();
Disposable disposableInstance = new Disposable() {
    @Override
    public void dispose() {
        isDisposed.set(true); (4)
    }

    @Override
    public String toString() {
        return "DISPOSABLE";
    }
};
```

--------------------------------

### Attach SampleSubscriber to a Flux

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/simple-ways-to-create-a-flux-or-mono-and-subscribe-to-it.html

Creates a SampleSubscriber instance and subscribes it to a Flux of integers from 1 to 4.

```java
SampleSubscriber<Integer> ss = new SampleSubscriber<Integer>();
Flux<Integer> ints = Flux.range(1, 4);
ints.subscribe(ss);
```

--------------------------------

### Implement a minimal BaseSubscriber (SampleSubscriber)

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/simple-ways-to-create-a-flux-or-mono-and-subscribe-to-it.html

Extends BaseSubscriber to perform bounded requests. Overrides hookOnSubscribe to print 'Subscribed' and request one element, and hookOnNext to print each value and request the next one.

```java
import org.reactivestreams.Subscription;

import reactor.core.publisher.BaseSubscriber;

public class SampleSubscriber<T> extends BaseSubscriber<T> {

	@Override
	public void hookOnSubscribe(Subscription subscription) {
		System.out.println("Subscribed");
		request(1);
	}

	@Override
	public void hookOnNext(T value) {
		System.out.println(value);
		request(1);
	}
}
```

--------------------------------

### Method that throws IOException

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/error-handling.html

A conversion method that throws an IOException for values greater than 3. Used in the subsequent map example.

```java
public String convert(int i) throws IOException {
    if (i > 3) {
        throw new IOException("boom " + i);
    }
    return "OK " + i;
}
```

--------------------------------

### Imperative dynamic fallback value with try-catch

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/error-handling.html

Imperative example of computing a fallback value from an exception, wrapping the error in a MyWrapper.

```java
try {
  Value v = erroringMethod();
  return MyWrapper.fromValue(v);
}
catch (Throwable error) {
  return MyWrapper.fromError(error);
}
```

--------------------------------

### Flux.interval(Duration)

Source: https://projectreactor.io/docs/core/release/reference/apdx-operatorChoice.html

Emits a tick (a long value starting from 0) at regular time intervals, using the specified period.

```APIDOC
## Flux.interval(Duration)

### Description
Emits a tick (a long value starting from 0) at regular time intervals, using the specified period.

### Method
- Flux.interval(Duration)

### Parameters
- **period** (Duration) - Required - The interval between emissions.

### Returns
- Flux<Long>
```

--------------------------------

### Output of state-based generate

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/programmatically-creating-sequence.html

The sequence generated by the preceding state-based generate example, showing the multiplication table of 3 from 0 to 10.

```java
3 x 0 = 0
3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
3 x 4 = 12
3 x 5 = 15
3 x 6 = 18
3 x 7 = 21
3 x 8 = 24
3 x 9 = 27
3 x 10 = 30
```

--------------------------------

### Output of SampleSubscriber

Source: https://projectreactor.io/docs/core/release/reference/coreFeatures/simple-ways-to-create-a-flux-or-mono-and-subscribe-to-it.html

Shows the expected console output when the SampleSubscriber is subscribed to a Flux of 1 to 4.

```java
Subscribed
1
2
3
4
```
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