Java 8 chained method reference?

Question

Suppose there is a typical Java Bean:

class MyBean {
    void setA(String id) {
    }

    void setB(String id) { 
    }

    List<String> getList() {
    }
}

And I would like to create a more abstract way of calling the setters with the help of a BiConsumer:

Map<SomeEnum, BiConsumer<MyBean, String>> map = ...
map.put(SomeEnum.A, MyBean::setA);
map.put(SomeEnum.B, MyBean::setB);
map.put(SomeEnum.List, (myBean, id) -> myBean.getList().add(id));

Is there a way to replace the lambda (myBean, id) -> myBean.getList().add(id) with a chained method reference, something like (myBean.getList())::add or myBean::getList::add or something else?

Answer 1

No, method references do not support chaining. In your example it wouldn’t be clear which of the two methods ought to receive the second parameter.

---

But if you insist on it…

static <V,T,U> BiConsumer<V,U> filterFirstArg(BiConsumer<T,U> c, Function<V,T> f) {
    return (t,u)->c.accept(f.apply(t), u);
}

…

BiConsumer<MyBean, String> c = filterFirstArg(List::add, MyBean::getList);

The naming of the method suggest to view it as taking an existing BiConsumer (here, List.add) and prepend a function (here, MyBean.getList()) to its first argument. It’s easy to imagine how an equivalent utility method for filtering the second argument or both at once may look like.

However, it’s mainly useful for combining existing implementations with another operation. In your specific example, the use site is not better than the ordinary lambda expression

BiConsumer<MyBean, String> c = (myBean, id) -> myBean.getList().add(id);