使用 Flux.handle() 时如何指定 generics

Question

As title, I don't know how to specify the generics when I using Flux.handle() . It will return a Flux<Object> after the handle() method like below example.

Flux.range(0, 10) // 1
        .handle((x, sink) -> {
            if (x % 2 == 0)
                sink.next(x);
        }) // 2
        .map(o -> Integer.valueOf(o.toString()))
        .subscribe(System.out::println);

It's a simple example to express the problem I'm facing so please don't care whether the content could be better.

The IDE shows Flux<Integer> at 1 and Flux<Object> at 2, so I need to add a map() method to transform the type which I want to use.

Is there any way to specify the return type without using map() ?

Answer 1

You can use a type witness:

Flux.range(0, 10)
    .<Integer>handle((x, sink) -> {
        if (x % 2 == 0)
            sink.next(x);
    });

This resolves to Flux<Integer>

This is a deficiency in Java's type inference, rather than a specific flaw of this class. Type witnesses are Java's way of explicitly declaring the generic type parameters, rather than relying on them being inferred.