How can we process asynchronously in Java?

The supplyAsync method is defined in the CompletableFuture class. The CompletableFuture class is defined in the java.util.concurrent package. To import the CompletableFuture class, we use the following import statement:

import java.util.concurrent.CompletableFuture;

`supplyAsync(Supplier<U> supplier)`

The supplyAsync method considers the passed Supplier as a task to be completed asynchronously. By default, the task is executed asynchronously in ForkJoinPool.commonPool(). This method returns a new CompletableFuture, and this value is received by invoking the supplied Supplier.

Syntax

public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)

Parameters

Supplier<U> supplier: This is the task that needs to be executed.

Return value

This method returns a new CompletableFuture.

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
public class Main {
    private static String process(){
        sleep(1000);
        System.out.println("Current Execution thread where the supplier is executed - " + Thread.currentThread().getName());
        return "Hello Educative";
    }
    private static CompletableFuture<String> createFuture(){
        return CompletableFuture.supplyAsync(Main::process);
    }
    private static void sleep(int millis){
        try {
            Thread.sleep(millis);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        CompletableFuture<String> stringCompletableFuture = createFuture();
        String value = stringCompletableFuture.get();
        sleep(3000);
        System.out.println("Completed Processing. Returned value - " + value);
    }
}

Code explanation

Lines 1–2: We import the relevant packages and classes.
Lines 6–10: We define a function called process, which prints the thread that executes this function. The function then sleeps for one second, and returns a string.
Lines 12–14: We define a function called createFuture. This function uses the supplyAsync() method to run the process() method in the common pool of ForkJoinPool. This function returns a CompletableFuture.
Lines 16–22: We define a function called sleep(), which makes the current thread sleep for the given number of milliseconds.
Line 25: We get the CompletableFuture by invoking the createFuture method.
Line 27: We retrieve the value that is returned by the process supplier function, using the get() method.
Line 29: We invoke the sleep function on the main thread.
Line 31: We print the value that is returned by the supplyAsync() method.

License: Creative Commons-Attribution-ShareAlike 4.0 (CC-BY-SA 4.0)

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