Java 8 Optional orElse orElseThrow inconsistent

Question

If a is Optional[123] and b is Optional[empty].

a.orElse(b.orElseThrow(() -> new UnexpectedInternalException(
                    "Error")))

Why does it throw?

What did you expect it to do? The `orElseThrow()` method is explicity designed to throw if your `Optional` is absent... — fge, Aug 01 '16 at 11:55

score 5 · Answer 1 · answered Aug 01 '16 at 11:55

5

Because parameters are evaluated first. This has nothing to do with Optional...

answered Aug 01 '16 at 11:55

Daniel David Kovacs

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score 5 · Accepted Answer · answered Aug 01 '16 at 11:55

5

orElse() is a method, and before that method is executed, its arguments are evaluated. In this case the evaluation of the argument (b.orElseThrow(() -> new UnexpectedInternalException("Error"))) throws an exception.

answered Aug 01 '16 at 11:55

Eran

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Java 8 Optional orElse orElseThrow inconsistent

2 Answers2