Illustration of thenCompose method of CompletableFuture

ThenComposeExample.java

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

public class ThenComposeExample {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {
            try { // delaying the thread by 2 seconds
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                throw new IllegalStateException(e);
            }
            return "Hello";
        }).thenCompose(msg -> CompletableFuture.supplyAsync(() ->
                msg + " World!")); // thenCompose() receives a fn to return the result of the same type
        // get() blocks and gets the result of the Future
        System.out.println(completableFuture.get());
    }
}