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Java CompletableFuture acceptEither()

By Arvind Rai, May 26, 2019
Java CompletableFuture implements CompletionStage and Future interfaces. CompletableFuture.acceptEither is inherited from CompletionStage. The acceptEither method returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied action.
Find the method declaration of acceptEither method from Java doc.
CompletionStage<Void> acceptEither(CompletionStage<? extends T> other, Consumer<? super T> action) 
The parameter other is the other CompletionStage.
The parameter action is the action to perform before completing the returned CompletionStage.
Find the examples.
Example-1:
AcceptEitherDemo1.java
package com.concretepage;
import java.util.concurrent.CompletableFuture;
public class AcceptEitherDemo1 {
  public static void main(String[] args) {
     CompletableFuture.supplyAsync(() -> "Welcome ABC")
        .acceptEither(CompletableFuture.supplyAsync(() -> "Welcome XYZ"), s -> System.out.println(s));
  }
} 
Output
Welcome ABC 
As we know that acceptEither method is executed with the result of either this or other given stage, whichever completes normally earlier. So in our example sometimes the output will be "Welcome ABC" and sometimes the output will be "Welcome XYZ".
Example-2:
AcceptEitherDemo2.java
package com.concretepage;
import java.util.concurrent.CompletableFuture;
public class AcceptEitherDemo2 {
  public static void main(String[] args) {
	
    CompletableFuture<String> cfuture = CompletableFuture.supplyAsync(() -> getA());
    
    CompletableFuture<String> otherCFuture = CompletableFuture.supplyAsync(() -> getB());
    
    CompletableFuture<Void> cf = cfuture.acceptEither(otherCFuture, s -> System.out.println(s));
    
    cf.join();
  }
  private static String getA() {
    try {
        Thread.sleep(500);
    } catch (InterruptedException e) {
        System.err.println(e);
    }	
	return "Mahesh";
  }
  private static String getB() {
    try {
      Thread.sleep(400);
  } catch (InterruptedException e) {
      System.err.println(e);
  }		
	return "Krishna";
  }  
} 
Output
Krishna 
In the above example we can see that otherCFuture will complete earlier than cfuture because getB() will complete earlier than getA() method. Hence acceptEither method will be executed with the result of otherCFuture completion stage.

References

Class CompletableFuture
Interface CompletionStage
POSTED BY
ARVIND RAI
ARVIND RAI
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