Callable

Runnable과 유사하지만 Callable은 반환값을 가집니다.

Callable

public interface Callable<V> {
    V call() throws Exception;
}

Callable은 선언한 객체를 리턴해 줍니다. Thead에는 FutureTask와 함께 사용하고, Executor에는 그대로 사용하면 됩니다

Thread이 시작되면 Callable에 작업 전달을 하고 응답 값은 future나 futrueTask에 전달이 됩니다.

Main Thread에서 값을 꺼낼때는 Callable에서 받아온 Future&FutureTast의 응답값을 주게 됩니다.

Thead

public class CallableWithThead implements Callable<String> {
    @Override
    public String call() throws Exception {
        return "I'm Callable";
    }
}

public class Main {
    public static void main(String[] args) {
        FutureTask<String> futureTask = new FutureTask<String>(new CallableWithThead());
        Thread thread = new Thread(futureTask);
        String result = futureTask.get();
    }
}

Executor

public class CallableWithExecutor implements Callable<String> {
    @Override
    public String call() throws Exception {
        return "I'm Callable";
    }
}

public class Main {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newSingleThreadExecutor();
        Future<String> future = executor.submit(new CallableWithExecutor());
        String result = future.get();
    }
}

Improve Future

향상된 Future엔 CompletableFuture 가 존재한다.

runAsnyc : return X supplyAsync : return 0 두가지로 작업을 실행할 수 있다.

public class CallbackSupplier implements Supplier<String> {
    @Override
    public String get() {
        return "I'm Supplier";
    }
}
public class CallbackRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("I'm Runnable");
    }
}

public class Main {
    public static void main(String[] args) {
        CompletableFuture<Void> runAsync = CompletableFuture.runAsync(new CallbackRunnable());
        CompletableFuture<String> supplyAsync = CompletableFuture.supplyAsync(new CallbackSupplier());

        Void noResult = runAsync.get();
        String result = supplyAsync.get();
    }
}

추가적으로 CompleteFuture에는 thenApply, thenAccept, thenRun을 사용하여작업을 연결해 줄 수 있다.

CompletableFuture<Void> runAsync = CompletableFuture.runAsync(new CallbackRunnable())
        .thenRunAsync(new CallbackRunnable());
CompletableFuture<String> supplyAsync = CompletableFuture.supplyAsync(new CallbackSupplier())
        .thenApply(s -> s + " and thenApply")
        .completeAsync(() -> "I'm completeAsync")
        .exceptionallyAsync(throwable -> "I'm exceptionallyAsync");

Void noResult = runAsync.get();
String result = supplyAsync.get();

thenCompose, thenCombine 으로 작업을 조합할 수도 있다.

CompletableFuture<String> supplyAsync = CompletableFuture.supplyAsync(new CallbackSupplier())
  .thenCombineAsync(CompletableFuture.supplyAsync(new CallbackSupplier()), (s1, s2) -> s1 + s2)
  .thenComposeAsync(s -> CompletableFuture.supplyAsync(() -> s + " and thenComposeAsync"));

지금 까지와 동일한 Printer를 예제로 사용

How do code?