Java List that conditional adds Optional

Question

Is there a library (e.g. Apache, Guava) that provides a List<T> with a method

void add(Optional<T> element)

that adds the element if it is present, (and is a no-op if !element.isPresent())? Obviously easy to implement, but it seems like such an obvious thing it seems someone might have done it already.

`Optional` as a method parameter seems to be discouraged, so chances are it is not implemented in popular libraries. Beside that, it's probably easier to just do `element.ifPresent(list::add)` — ernest_k, Dec 02 '18 at 19:22
Would you mind thinking about accepting an answer if it satisfies you ? ;) — azro, Feb 13 '19 at 09:59

azro · Accepted Answer · 2019-11-01T19:35:04.250

14

Instead of list.add(optio) you just need :

optio.ifPresent(list::add);

Example :

Optional<Integer> optio = Optional.ofNullable(Math.random() > 0.5 ? 52 : null);
List<Integer> list = new ArrayList<>();

optio.ifPresent(list::add);
System.out.println(list);                 //50% of [52], 50% of []

edited Nov 01 '19 at 19:35

answered Dec 02 '18 at 19:31

azro

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I personally think this is much more readable than `CollectionUtil.add(list, optio)`. +1 – Boris the Spider Dec 02 '18 at 19:35

score 2 · Answer 2 · answered Dec 02 '18 at 19:42

Obviously easy to implement, but it seems like such an obvious thing it seems someone might have done it already.

Well, sometimes the obvious things are the things that are left out as they're simple. Nevertheless, this is not something that's available in the Java standard library and don't see it anytime soon either due to the fact that Optionals were intended to be used as method return types instead of method parameters.

Also, "if this method were to be available" then it would require yet another add method overload polluting the API when it would be simple to do as @azro suggests for example.

Java List that conditional adds Optional

2 Answers2