What is CompletableFuture.thenRun() in Java?
thenRun() is an instance method of the CompletableFuture. It executes a runnable once the CompletableFuture is in the completed stage. It has no access to the result of the CompletableFuture to which it is attached.
The thenRun method is defined in the CompletableFuture class, which is defined in the java.util.concurrent package. To import the CompletableFuture class, we use the following import statement:
import java.util.concurrent.CompletableFuture;
Syntax
public CompletableFuture<Void> thenRun(Runnable action)
Parameters
Runnable action: It is the runnable action to be run.
Return value
This method returns a new CompletableFuture.
Code
import java.util.concurrent.*;public class Main {static void sleep(int millis){try {Thread.sleep(millis);} catch (InterruptedException e) {e.printStackTrace();}}static void executionThread(){System.out.println("Thread execution - " + Thread.currentThread().getName());}public static void main(String[] args){CompletableFuture<String> completableFuture1 = CompletableFuture.supplyAsync(() -> {sleep(1000);String stringToPrint = "Educative";System.out.println("----\nsupplyAsync first future - " + stringToPrint);executionThread();return stringToPrint;});Runnable runnable = () -> System.out.println("Runnable executed");completableFuture1.thenAccept(System.out::println).thenRun(runnable);sleep(2000);}}
Explanation
- Line 1: We import the relevant packages and classes.
- Lines 5 to 11: We define a function called
sleep(), which makes the current thread sleep for the given amount of milliseconds. - Lines 13 to 15: We define a function called
executionThread(), which prints the current thread of execution. - Lines 19 to 25: We create a completable future called
completableFuture1using thesupplyAsyc()method. We do this by passing a supplier that sleeps for 1 second, invokes theexecutionThread()method, and returns a string value. - Line 27: We define a runnable to execute after the completion of
completableFuture1. - Line 29: Once
completableFuture1is complete, we print the value returned by the future using thethenAccept()method. Then, the runnable is executed. - Line 30: The main thread sleeps for 2 seconds.
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