単純シミュレーションjava非同期コールバックモード

// 
public class Test {
    public static void main(String[] args) {
        ExecutorService executorService= Executors.newSingleThreadExecutor();
        System.out.println("A tells B to do something");
        CompletableFuture future = CompletableFuture.supplyAsync(() -> {
            try {
                System.out.println("B is doing something");
                Thread.sleep(5000);
                return "B has done something";
            } catch (InterruptedException e) {
                return "B died";
            }
        },executorService);
        executorService.shutdown();
        future.thenAccept(System.out::println);
        System.out.println("A continues to do other thing");
    }
}

//Future 
public class CompletableFuture {
    private final Object object = new Object();
    private String result;
    private Supplier supplier;
    private ExecutorService executorService = Executors.newSingleThreadExecutor();
    private boolean isComplete;

	private CompletableFuture() {
        
    }
    
    public void setSupplier(Supplier supplier) {
        this.supplier = supplier;
    }

    public void thenAccept(Consumer consumer) {
        executorService.submit(() -> {
            synchronized (object) {
                try {
                    while (!isComplete) {
                        object.wait();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            consumer.accept(result);
        });
        executorService.shutdown();
    }

    public void process() {
        result = supplier.get();
        synchronized (object) {
            isComplete = true;
            object.notify();
        }
    }

    public static CompletableFuture supplyAsync(Supplier supplier, ExecutorService executorService) {
        CompletableFuture future = new CompletableFuture();
        future.setSupplier(supplier);
        executorService.submit(future::process);
        return future;
    }
}

// 
public interface Consumer {
    void accept(String s);
}

// 
public interface Supplier {
    String get();
}