How to throw an exception using lambda expression

Question

I need to throw an exception if array contains a negative number.

What is best practices to do that using java8 features ?

Integer array = {11, -10, -20, -30, 10, 20, 30};

array.stream().filter(i -> i < 0) // then throw an exception

you should not throw an exception in a stream processing, that's an anti-pattern — Govinda Sakhare
– Govinda Sakhare, Commented Dec 27, 2020 at 14:43
@GovindaSakhare Thanks for the information. Have you got a source for that or a place to read more, please? — Anonymous
– Anonymous, Commented Dec 27, 2020 at 16:35

Youcef LAIDANI · Accepted Answer · 2020-12-27 14:50:41Z

3

You can use use Stream::anyMatch which return a boolean then if true thrown an exception like this:

boolean containsNegativeNumber = array.stream().anyMatch(i -> i < 0);
if (containsNegativeNumber) {
    throw new IllegalArgumentException("List contains negative numbers.");
}

Or directly as this:

if (array.stream().anyMatch(i -> i < 0)) {
    throw new IllegalArgumentException("List contains negative numbers.");
}

answered Dec 27, 2020 at 14:50

Youcef LAIDANI

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1 Comment

Andres Sacco Over a year ago

I think the second approach is great because you don't use any variable to throw the exception

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