Java 泛型 : vs 捕获

Question

我正在尝试模拟 ScheduledExecutorService，但我在使用泛型时遇到了麻烦。

这是一个片段:

ScheduledFuture<?> future = mock(ScheduledFuture.class);

ScheduledExecutorService scheduledExecutorService = 
Mockito.mock(ScheduledExecutorService.class);

when(scheduledExecutorService.schedule(Mockito.any(Runnable.class), anyLong(), any(TimeUnit.class))).thenReturn(future);

这不会编译并出现以下错误:

Error:(20, 109) java: no suitable method found for 
  thenReturn(java.util.concurrent.ScheduledFuture<capture#1 of ?>)
method org.mockito.stubbing.OngoingStubbing.thenReturn(java.util.concurrent.ScheduledFuture<capture#2 of ?>) is not applicable
  (argument mismatch; java.util.concurrent.ScheduledFuture<capture#1 of ?> cannot be converted to java.util.concurrent.ScheduledFuture<capture#2 of ?>)
method org.mockito.stubbing.OngoingStubbing.thenReturn(java.util.concurrent.ScheduledFuture<capture#2 of ?>,java.util.concurrent.ScheduledFuture<capture#2 of ?>...) is not applicable
  (argument mismatch; java.util.concurrent.ScheduledFuture<capture#1 of ?> cannot be converted to java.util.concurrent.ScheduledFuture<capture#2 of ?>)

如果我在声明 ScheduledFuture 时不使用泛型，它会在编译时出现警告。

 ScheduledFuture future 

有什么正确的方法吗？我的意思是，有没有我可以使用的通配符，这样它就可以在没有警告的情况下进行编译？

Answer 1

以下工作类型正确:

<T> ScheduledFuture<?> thenReturnMockFuture(
    OngoingStubbing<ScheduledFuture<T>> stubbing) {
  // Declare a local abstract class, so that future is type-correct.
  abstract class ScheduledFutureT implements ScheduledFuture<T> {}
  ScheduledFuture<T> future = mock(ScheduledFutureT.class);

  stubbing.thenReturn(future);
  return future;
}

然后这样调用:

ScheduledExecutorService scheduledExecutorService = 
    mock(ScheduledExecutorService.class);

ScheduledFuture<?> future = 
    thenReturnMockFuture(
        when(scheduledExecutorService.schedule(...)));

---

我想你也可以这样做(没有方法，但有抽象本地类):

ScheduledFuture<?> future = mock(ScheduledFutureT.class);
doReturn(future).when(scheduledExecutorService).schedule(...);

注意 the caveat那doReturn不是类型安全的，所以你只需要确保你正在调用一个确实返回 ScheduledFuture<?> 的方法。 .