[英]Type mismatch when extending CompletableFuture
I am trying to extend CompletableFuture
to do a thenCompose
after handle
, but I got a compiler error: 我试图延长
CompletableFuture
做thenCompose
后handle
,但我得到一个编译器错误:
Type mismatch: cannot convert from CompletableFuture(Object) to CompletableFuture(U)
This is my code: 这是我的代码:
public class MyCompletableFuture<T> extends CompletableFuture<T> {
public <U> CompletableFuture<U> handleAndCompose(BiFunction<? super T, Throwable, ? extends U> fn) {
return super.handle(fn).thenCompose(x->x);
}
}
For the record, I am trying to hide the thenCompose
used on this reponse which is basically: 作为记录,我试图隐藏此响应上使用的
thenCompose
,基本上是:
.handle((x, t) -> {
if (t != null) {
return askPong("Ping");
} else {
return x;
}
)
The signature of your method is incorrect. 您的方法签名不正确。 It should be:
它应该是:
public <U> CompletableFuture<U> handleAndCompose(BiFunction<? super T, Throwable, ? extends CompletableFuture<U>> fn) {
return super.handle(fn).thenCompose(x->x);
}
Note that the function given returns ? extends CompletableFuture<U>
注意给定的函数返回
? extends CompletableFuture<U>
? extends CompletableFuture<U>
instead of ? extends U
? extends CompletableFuture<U>
而不是? extends U
? extends U
. ? extends U
You could also accept as argument a more general CompletionStage
instead of a CompletableFuture
. 您也可以接受更通用的
CompletionStage
而不是CompletableFuture
作为参数。
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