This program is to show the manual completion of completablefuture.

ManualCompletionExample.java

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

class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {
            try {
                TimeUnit.SECONDS.sleep(1000);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
            return "Completed automatically";
        });
        if(completableFuture.isDone()){
            completableFuture.get();
        }else{
            completableFuture.complete("Completed manually");
        }
        System.out.println(completableFuture.get());
    }
}