实施 CompletableFuture 时出错 "CompletableFuture(Object) has private access in CompletableFuture"

Question

我正在按如下方式实施 CompletableFuture，但收到一条错误消息

CompletableFuture(Object) has private access in CompletableFuture

public CompletableFuture<A> init(B b) {

    C c = new C();  
    CompletableFuture<A> future = new CompletableFuture<A>(c);

    return future;
}

public class C implements Callable<A> {

    public A call() throws Exception {
        A a = new A();
        return a;
    }
}

我希望解决这个错误？

Answer 1

CompletableFuture class 中没有接受参数的 public 构造函数。最好使用 CompletableFuture.supplyAsync() 静态方法，它采用 Supplier 而不是 Callable:

CompletableFuture<A> future = CompletableFuture.supplyAsync(A::new);

或使用 lambda：

CompletableFuture<A> future = CompletableFuture.supplyAsync(() -> new A());

注意如果A构造函数抛出checked exception，你应该按Supplier接口不支持异常处理：

CompletableFuture<A> future = CompletableFuture.supplyAsync(() -> {
    try { return new A(); }
    catch(Exception ex) { throw new RuntimeException(ex);}
});

最后请注意，supplyAsync 不仅会创建 CompletableFuture，还会安排它在公共线程池中执行。您可以将自定义 Executor 指定为 supplyAsync 方法的第二个参数。如果你想创建 CompletableFuture 而不立即发送它来执行，那么你可能不需要 CompletableFuture.

实施 CompletableFuture 时出错 "CompletableFuture(Object) has private access in CompletableFuture"

Error saying "CompletableFuture(Object) has private access in CompletableFuture" when implementing CompletableFuture

intellij-idea

java-8

completable-future