如何将方法引用传递给协变参数

Question

Given we have the following classes an methods:

class Fruit {}
class Orange extends Fruit {}

void process(Consumer<? extends Fruit> action) {}
void eatOnlyOranges(Orange evt) {}

---

This compiles without warning.

    Consumer<Orange> consumer = this::eatOnlyOranges;
    process(consumer);

---

I want to allow this, but it doesn't compile?

    process(this::eatOnlyOranges);

Can I change the signature of process(Consumer<? extends Fruit> action) to make it work?

NOTE: Please assume that the implementation of process(..) will check if the given Consumer can handle the given Fruit . This detail is not relevant for this question.

Answer 1

Besides @EmersonCod's answer, changing the method signature to

<T extends Fruit> void process(Consumer< T > action) {
    // ...
}

seems to do the job.

Answer 2

您需要将Consumer转换为特定类型

process((Consumer<Orange>) this::eatOnlyOranges)