如何将单个元素列表转换为java 8可选

Question

How to nicely convert list containing one or zero elements to Optional?

The ugly code:

List<Integer> integers = new ArrayList<>();

Optional<Integer> optional = integers.size() == 0 ?
        Optional.empty() :
        Optional.of(integers.get(0));

Answer 1

You can use the Stream#findFirst() method, which:

Returns an Optional describing the first element of this stream, or an empty Optional if the stream is empty.

List<Integer> list = ...
Optional<Integer> optional = list.stream().findFirst();

Alternatively, with the same success you can also use the Stream#findAny() method.