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The CompletableFuture class in Java provides the thenAcceptBoth() method to perform an action when two CompletableFuture instances complete.
Introduction
The CompletableFuture.thenAcceptBoth() method is used to perform a specified action when both CompletableFuture instances complete. It takes a BiConsumer that processes the results of both futures and returns a new CompletableFuture that is completed when the action is finished.
thenAcceptBoth Method Syntax
The syntax for the thenAcceptBoth method is as follows:
public <U> CompletableFuture<Void> thenAcceptBoth(CompletionStage<? extends U> other, BiConsumer<? super T, ? super U> action)
- The method takes two parameters:
otherof typeCompletionStage<? extends U>, which is the otherCompletableFutureto combine with.actionof typeBiConsumer<? super T, ? super U>, which represents the action to perform on the results of both futures.
- The method returns a new
CompletableFuture<Void>that is completed when the action is finished.
Examples
Example 1: Printing Results of Two Asynchronous Tasks
In a scenario where you have two CompletableFuture instances that complete with different results, you might want to print both results when both futures complete.
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
public class ThenAcceptBothExample {
public static void main(String[] args) {
// Create two CompletableFuture instances
CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> "Hello");
CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> "World");
// Print the results of both futures using thenAcceptBoth
future1.thenAcceptBoth(future2, (result1, result2) -> System.out.println(result1 + " " + result2));
// Wait for the futures to complete
try {
future1.get();
future2.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
}
Output:
Hello World
Example 2: Task Management System
In a task management system, you might want to log the completion of two tasks when both tasks are completed.
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
public class TaskManagementSystem {
public static void main(String[] args) {
// Create two CompletableFuture instances for tasks
CompletableFuture<Task> taskFuture1 = CompletableFuture.supplyAsync(() -> new Task("Complete project report", 2));
CompletableFuture<Task> taskFuture2 = CompletableFuture.supplyAsync(() -> new Task("Email client updates", 1));
// Log the completion of both tasks using thenAcceptBoth
taskFuture1.thenAcceptBoth(taskFuture2, (task1, task2) ->
System.out.println("Tasks completed:\n" + task1 + "\n" + task2)
);
// Wait for the tasks to complete
try {
taskFuture1.get();
taskFuture2.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
}
class Task {
private String description;
private int priority;
public Task(String description, int priority) {
this.description = description;
this.priority = priority;
}
@Override
public String toString() {
return description + " (Priority: " + priority + ")";
}
}
Output:
Tasks completed:
Complete project report (Priority: 2)
Email client updates (Priority: 1)
Example 3: Merging Data from Two Sources
In a data processing application, you might want to merge data from two different sources when both sources have completed their data fetch.
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
public class DataMergeExample {
public static void main(String[] args) {
// Create two CompletableFuture instances for fetching data
CompletableFuture<String> dataFuture1 = CompletableFuture.supplyAsync(() -> "Data from source 1");
CompletableFuture<String> dataFuture2 = CompletableFuture.supplyAsync(() -> "Data from source 2");
// Merge the data from both sources using thenAcceptBoth
dataFuture1.thenAcceptBoth(dataFuture2, (data1, data2) ->
System.out.println("Merged data: " + data1 + " + " + data2)
);
// Wait for the data fetches to complete
try {
dataFuture1.get();
dataFuture2.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
}
Output:
Merged data: Data from source 1 + Data from source 2
Conclusion
The CompletableFuture.thenAcceptBoth() method in Java is used for performing actions that depend on the completion of two CompletableFuture instances. It is particularly useful in scenarios where you need to process and combine the results of multiple asynchronous computations, such as printing results, logging task completions, or merging data from different sources.
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